rough idle

[Guest whitey]

I have a OLDPA3 ED17 reading of 287 counts which is beyond the 255 max limit. This '88 Reatta has a rough idle when closed loop which is why I checked my diagnostics. I have no trouble code messages. Could this be a faulty knock sensor? The car has about 33k miles and has new wires, plugs and air filter. My in city gas mileage is low, about 11-12 mpg using the CRT numbers. I plan to change the O2 sensor and ignition coil pak as part of the tuneup but for now this knock sensor reading goes beyond normal...any thoughts?

[2seater]

I do not remember if my ED17 will count above 255 or not? In any case, it shouldn't be a problem unless you see that number increasing while the engine is idling. It is normal to get a number of knock counts simply from the act of starting the engine. If the counts are stable while the engine is idling, tap on the engine lift bracket or on one of the solid mounts for the alternator or power steering and see if the number increases. It takes a fairly sharp rap, and may actually cause a change in the idle if the ECM pulls the timing back in response to the knock. If the knock counter is stable at idle, but increases with a tap on the engine, the system is operating normally. A sharp rap will cause the counter to increase by many numbers, not just a single count.

By the way, I have found a couple of sensors that will read higher than the accepted "normal". I have seen air flow over 170 gm/sec and the BLM over 150 also. The O2 sensor can have a large influence on the fuel mileage if everything else is working reasonably well. Watch the O2 cross counts to see if the sensor is active.

[Guest whitey]

Thanks 2 seater. Guess I never paid much attention to knock sensor data until now. It looks like the sensor holds whatever number might be generated on startup or knock then resets only on shutdown. Today on restart the number was close to 500 counts, a couple of raps on the power steering bracket and it was reading 1000 then another rap and it reads and holds 1600 counts. Restart and the EB17 reads about 250 and holds. Guess it works. I'll look elsewhere for my rough idle causes after my O2 sensor and ign. coil arrive and are replaced.

[Ronnie]

Welcome to the forum whitey! You will receive lots of help here with your problems. You are in good hands with the knowledgeable folks here on the forum.

[Guest Mc_Reatta]

Welcome whitey!

While your Reatta has few miles and I wouldn't expect would have much build up on the IAC or MAF, I would suggest you pull, examine and clean both and replace. (do a tap test on the MAF too just in case) That doesn't cost anything and eliminates them as contributors to any driveability problems.

Also cleaning the positive and negative junction posts under the hood will ensure the electronics are getting clean power which eliminate strange gremlins from appearing that can give all sorts of intermittent problems. Again that doesn't cost anything and can't hurt. Ronnie's site has procedures for doing all of these.

But I think your replacing the O2 sensor and the ICM will probably yield good results, just not for free. Do the ICM swap by itself so that if it doesn't have any goo showing and doesn't eliminate your issue, you can keep it as a spare.

Edited June 13, 2012 by Mc_Reatta (see edit history)

[2seater]

Damn, I didn't notice you were a new member. As the others have said, welcome to the best forum on the net. There is s wealth of knowledge and help available. I don't know how long you have had your Reatta but I have not found the engine to be particularly smooth, hence the balance shaft Is the rough idle a new issue? What are the conditions for the city driving? Is the highway mileage considerably higher and how close is the readout to the actual calculated mileage at fillup? It can approach 30mpg in an extended run.

[Guest whitey]

I picked up this car recently. It is has a New Mexico history and a lot of that time was spent in hot storage. I expected the usual gasket shrinkage and rubber rot but this idle thing acts as though it is getting an accumulation of bad data which builds into a rough idle...sometimes shutter under load conditions when near idle conditions. Over all it starts quick, cold idle is 1000 rpm and relatively smooth acceleration. Once warm (200f) the idle under braking is rough but it never stalls, just makes you think that it will.

If I remove the battery cables, ground them to reset the gremlins, then the car idles relatively good when under braking and warmed up. After 20 miles driving the rough idle is back. This also happens whenever I replace a part.

All the normal tune up things have been done except for the O2 sensor not here yet but I have a hunch that will not fix my problem because it runs and starts too good even though it's getting only showing 10 to 11 mpg in the city. The O2 sensor readings shows .18 to .81 volts at idle and warmed up so that looks to be in range but I don't know what acceptible numbers are. I'm thinking if the idle gets right, the mpg will take care of itself. My IAC has been cleaned,the MAF replaced with rebuilt, wires, plugs and ignition coil pak . air filter , fuel filter are new and the intake decarbed, throttle body and EGR cleaned. The mpg is only city driving because the tire show slight dry rot sidewall separation and high speed would be unadvisable until I get them replaced. I've gone through all the diagnostic data and all the numbers fall within the range but I really don't know what normal is. You mention that the idle is never that smooth but does it feel like I discribed above or am I chasing a ghost and what else is left to fix or replace?

[Guest whitey]

Sorry 2seater, got carried away there..just like going to the confessional as a kid. You asked if the rough idle is a new thing. It was rough when I purchased the the car but there were a lot of things that needed replacement, most of which should have helped smooth the idle but only temporarily as noted in my windy message. If the problem didn't go and come back I would think it a balance problem. This feels to me like the ECM gets confused. And I realize the mpg thing is base on limited data and maybe that will work its way out but so far it seems to hold , albeit the CRT number, at 10 to 11 mpg.

[2seater]

I imagine you have a vacuum gauge. You may want to install it and see what it looks like cold and hot. I would suspect a possible vacuum leak. A small leak will be covered up by the richer conditions when the engine is cool and running open loop. My engine has been changed and fiddled with for years but it still has a reasonable 18"Hg idle vacuum, which drops to 17 when in gear. Run you hands over the vacuum hoses and if they come away black, the hose is deteriorating and likely porous. Check the pcv valve and the hoses at the upper rear of the engine that run toward the firewall. Idle quality is subjective and you don't mention that it is "hunting" so I'm guessing the IAC is operating properly. Ignition quality will have some effect as well as the spray pattern from the injectors. If you have a fuel pressure gauge, check that also. It should be in the low 40#'s range with the vacuum disconnected and drop by approx. 1/2 of the manifold vacuum gauge reading when the vacuum is reconnected to the regulator. The range mentioned for the O2 sensor is about right, but is usually easier to look at the cross counts to see how active it is. Ignition timing should be around 20 degrees at hot idle in park and jump up a little when in gear to help pick up the load on the engine. The BLM and fuel Integrator should stay right around 128 if everything is operating as it should. Substantial variation, high or low, will indicate if the ECM thinks it is running rich or lean.

[Guest whitey]

My timimg shows 20 degrees and fuel integrator 132. The BLM is 155...a little high. what does that mean? Actually I think your vacuum problem is probably right. Even though I did a check for loose or broken hoses, never thought about a porosity issue. These hoses are old. In fact, when I tried the Seafoam intake cleanse I couldn't get any measurable suction from the 1/2 in hose fitting located on the lower throttle body as per Ronnie's instructions. I was told by a mechanic not to expect much vacuum there because it just pulls fumes off the valve cover...so I let it go. Question, should there be a strong vacuum pull at that location?

[2seater]

If the BLM is maxed out @ 155, it is working, but the ECM thinks the engine is running lean. It has tried to add long term fueling to compensate for something, maybe unmetered air? I found porous hoses some years ago because I would save everything for possible reuse . When checking something vacuum operated with a hand vacuum pump I noticed it would bleed down. Checking the hose by itself showed the hose leaked. Low fuel pressure or plugged injectors can cause the ECM to try to add fuel also as well as an exhaust leak ahead of the O2 sensor.

The large fitting at the lower front of the throttle body is connected to the front valve cover and only allows air from ahead of the throttle to flow to the valve cover. There should be no appreciable vacuum on that port. At maximum throttle and air flow there will be a slight vacuum just due to intake filter restriction but it is not a vacuum port.

[Guest whitey]

Thanks for the leads....time to get dirty.

[Guest whitey]

Thanks for the leads....time to get dirty.

This '88 Reatta is a real pain. Even though it's been driven only 28,000 miles it seems to drive worse with every repair. I'm sure all it's problems, many of which I anticipated, are related to being stored in a hot climate for years by the original owner. It never throws a code showing a problem. The rough idle problem seems to come and go. When I last contacted this forum I was about to try some fixes. The latest repairs are: replaced the oxygen sensor with no improvement. I replaced the ignition coil because there was corrosion starting on the #1 terminal. No improvement. I tested the fuel pressure and it was jumping around at 35 to 40 lbs. Leaving the car run eventually showed a 12 lb reading. So fuel pump is going bad. I went to my local mechanic and had him confirm and drop the tank to replace. The old pump's rubber seals were starting to deteriorate really bad so I'm appreciative for that suggestion. Heat had certainly taken a toll here. I also asked the mechanic to check for vacuum leaks since I had found no obvious leaks. My vacuum reads 16" and steady when in PARK...not the greatest but in spec.. The mechanic got the same and he sprayed the hose looking for a idle response and got no change. I had this mechanic drive the car home a couple of times just to see if the repairs were a fix and he felt it was idle was OK and contributed my problems to the fuel pump which now give a steady 45 lbs. pressure. So here is the rub:

I drove the car around for 25 miles of level city driving to get a feel for the MPG's since the mechanic zeroed the readings. The MPG's started at 2 MPG and after the drive climbed slowly to 7.5 MPG...not so good but maybe it is just trying to average the low starting number so I think more driving should help the numbers, we'll see but this doesn't seem right. At one point in the drive test I ran the diagnosics (in PARK). Two things jumped out, the knock sensor ED17 showed 9999 and the BLM still show high at 255 so it thinks its lean and compensating rich. Turned the car off/on and the ED17 showed 857 so is it bad? got home and did the rap on the pipe test and it tested correctly..can't figure. Did a couple of restarts while it was warms to get more data and once I could not get the CRT to go into diagnostic mode. So I restarted and stalled right after the start. Got a ABS light and check engine. On next restart it stumbled, ran more rough but stayed running. Think it flooded that time because I could smell gas.

My general take on all this is that some times the car starts very quick and run good but the BLM is still 155 in PARK. Other time the car will stumble on a start (either warm or cold) and that signals a rougher idle will reappear. So it seems electrical to me but what do I know. I see no obvious corrosion on the wires or ground box (black) in engine compartment. Are there more grounds to clean? Could the ECM be the cause? Do ECM connectors go bad? Just don't know what's next. Any ideas?

Edited July 3, 2012 by whitey (see edit history)

[KDirk]

Whitey,

I can relate to your woes. I have a low mileage 88 (purchased with 36K about 1.5 years ago now) and went through all manner of problems getting it to run right. The first thing that sticks out in your most recent post are the knock sensor and BLM figures. These are WAY out of whack. The figures you posted are the actual maximum (theoretically) possible values for the respective data points. In actual operation, they should never read that high. This makes me think there is a communication problem to (or with) the ECM and it is defaulting these values to their max. Not sure why it would do that, as I find it highly unusual that it would fill in those values as fallback defaults but also cannot see that the car would be running at all with those kinds of data values if they are really that high.

One thing, as stupidly obvious as it may seem, is to verify the routing of your spark plug wires to their respective cylinders. As a helpful hint, the snap-on two-wire connector for each fuel injector is imprinted with it's cylinder number. Just use these numbers to match each wire back to it's correct coil. When I bought my car, the evens and odds were reversed; and the kicker is that the factory manual states that is how they should be hooked up. Obviously, this is an error in the service manual, but I would venture to guess others have made the mistake of mis-routing the wires simply by following what the manual says.

If that checks out, then I am not sure what to suggest next as reading your previous posts here, you seem to have covered all the usual suspects already (vacuum leak, fuel issues, etc.). I will say that I had a bad intake manifold gasket and EGR valve gasket (both recently replaced) and those cleared up the last of my residual rough idle/stalling problems; my car is running great now. My point is not to discount the possibility of a vac leak, even though you are within spec (albeit a bit low perhaps) at 16".

Pay special attention to rubber vacuum lines especially short pieces that make bend connections between rigid portions of line. I found several on my car that were in poor condition due to dry rot. One was cracked, and was affecting my cruise control not holding speed intermittently. I replaced every piece of rubber vacuum line I could find, as age and heat had turned most of it marginal in condition. Hopefully you will find your issue before too long. These can be very frustrating, especially when several repairs have already been made and no improvement is gained.

Edit: Also see Ronnie's reply (next post) and verify all your main power and ground connections. Many GM vehicles that are heavy on electronics (and the Reatta definitely fits that bill) get strange symptoms if the ECM, BCM and other key modules are not getting clean solid power. My 95 Deville will throw all kinds of random codes sometimes if the battery connections are just very slightly loose (stupid side terminals!). Get 'em tight, and some dielectric grease is also recommended to keep corrosion at bay.

KDirk

Edited June 28, 2012 by KDirk (see edit history)

[Ronnie]

[Guest whitey]

Thanks for the diagram via Ronnie...been looking for this everywhere. Looks like I have more connections to clean.

I did check the spark plug wires and they all match the injectors,really never noticed the numbers on the snap-ons, thanks. Also, my intake manifold gasket /seal was replaced when I first bought the car a few months ago,since it was showing signs of leaking back then. Now the EGR gasket might be good lead that I will try. As for the vacuum, did you replace hoses under the dash also and if so is there a diagram showing where all these are located? I didn't see such a thing in the service manual.

The one thing that bothers me most about this is the quick start up versus the stumble start up. I think the stumble is a partial flood effect that throws off the ECM logic and rough idle follows for a while then becomes more reasonable. It is a ramdom starting thing. What could throw an enrichment signal on 1st crank ....sometimes. Has anyone complained that the fuel pump sender unit to be an issue. The mechanic who installed it mention that after the initial install the new pumps' sending unit was not working because the car would quit after a start. Later he said that was not the cause but rather a connection/wire harness issue that he fixed but did not elaborate. I'm wondering again if connections are the problem.

[2seater]

The knock sensor should be monitored while running and driving to see if the number is increasing steadily. You cannot use a snapshot view of that number as it may increase for a couple of different reasons even if everything is operating normaly. Just the act of starting the engine will cause the number to increase and is perfectly normal. It should not increase just in normal low load driving. The Block Learn and Fuel Integrator should be monitored over a wide range of driving and extended miles. If just observed while idling in park, you are seeing only one cell in the fueling chart. It does take time for it to adjust to new operational conditions and if you have recently disconnected the battery, it will start from the default setting and change from there. Changes do not occur instantly (except the battery reset), and it will need closed loop operation for it to start making adjustments. You should be able to see a trend fairly quickly but it does take a little time.

I have not had any issues with the EGR on my Reatta, but I have had issues with a Ford Ranger. It was stuck partially open and just killed the idle quality, and since it has vacuum assist brakes, that suffered as well. Idle vacuum was down in the 10"-12" range and jumped up to just over 20" after the EGR was repaired. It is a different system than GM's but the effects can be dramatic. Yours does not seem to have a serious problem with EGR but you may try cycling the three valves in the EGR using the overide section of diagnostics to see how the engine responds.

It is possible for the ECM to be go bad, maybe a defective solder joint or some sort of intermittant. The one thing the ECM does not do a good job of diagnosing is itself. If all other common and suggested issues are inspected, it may be possible the ECM needs to be replaced. If so, do not forget to transfer the EEprom to the new ECM.

[wws944]

This '88 Reatta is a real pain. Even though it's been driven only 28,000 miles it seems to drive worse with every repair...

Don't despair. When I started in on my car three years ago, it had idle problems with only 9K miles. There were a couple of issues, but the main one was a failing fuel pressure regulator. (Noted fuel in the FPR vacuum line.)

My vacuum reads 16" and steady when in PARK...not the greatest but in spec..

I'd suggest working on this. Vacuum in my Reatta measures a solid 20". Gotta be a vacuum leak somewhere.

[Guest whitey]

Don't despair. When I started in on my car three years ago, it had idle problems with only 9K miles. There were a couple of issues, but the main one was a failing fuel pressure regulator. (Noted fuel in the FPR vacuum line.)

I'd suggest working on this. Vacuum in my Reatta measures a solid 20". Gotta be a vacuum leak somewhere.

So far it looks like I need to check for the FPR leakage and do a EGR gasket set replacement in an effort to find the vacuum leak. Thanks for the leads.

[Guest whitey]

The knock sensor should be monitored while running and driving to see if the number is increasing steadily. You cannot use a snapshot view of that number as it may increase for a couple of different reasons even if everything is operating normaly. Just the act of starting the engine will cause the number to increase and is perfectly normal. It should not increase just in normal low load driving. The Block Learn and Fuel Integrator should be monitored over a wide range of driving and extended miles. If just observed while idling in park, you are seeing only one cell in the fueling chart. It does take time for it to adjust to new operational conditions and if you have recently disconnected the battery, it will start from the default setting and change from there. Changes do not occur instantly (except the battery reset), and it will need closed loop operation for it to start making adjustments. You should be able to see a trend fairly quickly but it does take a little time.

I have not had any issues with the EGR on my Reatta, but I have had issues with a Ford Ranger. It was stuck partially open and just killed the idle quality, and since it has vacuum assist brakes, that suffered as well. Idle vacuum was down in the 10"-12" range and jumped up to just over 20" after the EGR was repaired. It is a different system than GM's but the effects can be dramatic. Yours does not seem to have a serious problem with EGR but you may try cycling the three valves in the EGR using the overide section of diagnostics to see how the engine responds.

It is possible for the ECM to be go bad, maybe a defective solder joint or some sort of intermittant. The one thing the ECM does not do a good job of diagnosing is itself. If all other common and suggested issues are inspected, it may be possible the ECM needs to be replaced. If so, do not forget to transfer the EEprom to the new ECM.

2seater

The knock sensor does seem to work as you say when driving and it has started out at some reasonable number...like 300 to 900 depending on the what it first senses on the crank. It holds steady while driving. I understand what you are saying and appreciate it but the knock sensor issue has resurfaced very recently,(with a bang) when the car really seems out of sync (i. e. rough idle and terrible MPGs and stumble on startup), I have seen a reading of 9999 which to me looks like a default from the computer. On a restart, the reading will return to be much less as in the 300 to 900 reasonable range. This has happened on 2 occasions in the past 10 starts. I don't think you can bang on the engine hard enough or often enough to get a reading that high so I was looking for a reason why a 9999 would occur. If I can find the reason then maybe I'll get closer to the core problem with the system, thinking the knock sensor irregularities will go away when that problem is located.

The fuel integrator has never been out of range, neither in PARK or on the road. 125-132 always. The Block learn is a puzzle because it also always looks good while driving....close to 125-135 but as soon as you put the car in PARK in shows 152-155. Closed loop or open loop, always shows 152-155 immediately and stays there until you start driving again. It just wants to be rich when in PARK. Now maybe I am expecting a 128 range reading in PARK because of what I read on the FORUM and in the service manual but maybe there is some leeway here and I'm curious as to what other Reatta owners see. My low MPG's started this scrutiny. PARK operation suggests vacuum issues which have not been obvious except for the 16" steady max draw and I will look at them more closely (see previous post).

The ECM? I have a spare but it's not complete being without the updated "88 PROM and MemCal which I can't seem to locate. It doesn't make much sense to me to replace the ECM without it being updated and whole. Any sources out there from the members? Again, thanks for all who have offered their time and help.

Edited June 29, 2012 by whitey (see edit history)

[KDirk]

Whitey-

I might follow up with the following:

1) The EGR valve has two gaskets. One is between the EGR valve itself and the adapter mount. The second is between the adapter mount (held on by two 10mm bolts) and the manifold. Both might be suspect, and are inexpensive so are worth changing just as a PM item on an older car where the condition is unknown.

2) I did not replace any vacuum hose inside the car (yet) only under the hood. I have not looked closely at the FSM to see if there is any detailed diagram of the in-dash vacuum line/routing. No reason to, as it stands now my car is running great - fuel economy is still sub-par IMO. Of course, it is hot as hell here in St. Louis (108 today!) and we are on summer fuel mixture which impacts it. I cannot find anything wrong with the car (ok, maybe the guy in the drivers seat pushing the pedal and running the AC on max) to account for lowish MPG's. In any case, I have whipped my vacuum problems for now.

If you haven't checked the FPR previously, this is highly recommended. Be ready for some sticker shock if it needs replacement. And, as much as I hate to point to the ECM (seems I like to fault it a lot for problems I see posted here, like a pediatrician handing out ADHD diagnoses) it is something to look at if all other items have been addressed. With your low vacuum reading, I think that needs further examination before calling the ECM suspect.

KDirk

[Guest whitey]

2seater

Your suggestion to override the EGR delves into unfamiliar territory for me. Can you suggest a reasonable approach to this test. Say if I were to override to a value of 50, is the effect I seek when all 3 solenoids are adjusted or one at a time? Also, can I go back to the ECM data ED20 (BLM) and look for a an improved value or must I stay on the override page and just feel a better idle? When I'm done with the test must I backout of the override to return to where I started or does the override just go away when I return to the data screen? I'm a rookie.

Also, is the purpose of a snapshot just to record data points at a point in time or can it be used by the ECM as a reference? The reason I ask this is that when I ground my battery cables to reset, the ECM and run the car for 10 miles or so to learn, I get my best idle(almost smooth) and mileage(15MPG city) performance that has yet to be corrupted by subsequent starts. Recording these fresh parameters for the ECM to reference would be ideal if it works that way. Still a rookie.

[2seater]

If it runs better after you reset (battery disconnect), then something is causing the programming to adjust towards readings that are out of range and possibly causing the problems you see. Everything starts out at the default values, designed to get the car running and be safe, which usually means a little rich. If the BLM does not reset to 128 then you may have a defect in the ECM or Prom. I am not sure about the interaction between the ECM and Prom, but I do know the operating limits of the INT/BLM can be changed in the Prom program to adjust the readout to the normal expected range. I have used various sizes of injectors, from stock 19# to aftermarket 30#, for my turbo experimenting, and if the Prom is not adjusted, I have seen readings under 100 and over 150. As long as the Integrator is around the target range of operation, the long term BLM adjustment has been succesful. Not to say it is proper, but it is doing its best to protect everything else.

I do not remember exactly how the EGR overide reacts when used and I have lent my car out for a few days so I cannot try it to be sure of what it does. The three individual pintle valves in the EGR control different size orifices and are activated in various combinations to get the desired exhaust flow commanded by the ECM. They are actually three discrete solenoid valves packaged on a single housing. There should not be any flow at idle. You can use a small piece of aluminum beverage can to make a temporary block under the lower mount. The valves for the EGR actually contact the plate it is mounted to, not the gasket itself. I do know that I have tried what I would call a cylinder balance test by cycling the individual injectors on and off. I disconnect the IAC so it cannot adjust engine idle and see what happens to the engine rpm as each cylinder in turn is deactivated. You can also overide the IAC first to set some rpm you would like first. I do not know of any way to toggle between overide and operating data directly. You get one or the other at a time.

As far as I know, the snapshot is used to try to capture data for you at the time of a fault. The ECM doesn't care about it. I don't believe you are somehow forcing the ECM to adjust to your will If I understand from your post, the car is running better, and indicating improved mileage, and it is remembering the changes? All I can tell you for sure is my car makes most of the large adjustments on the drive home from storage (15 miles), but it will always be tweaking on the adjustable stuff, it's just the way it is.

[KDirk]

The EGR test is accessed from on-screen diagnostics. I don't have my FSM with me at the moment, so cannot type out the exact procedure and ECM override number to do it, but each of the three solenoids can be overridden individually (turned on and back off) in service mode. This can only be done with transmission in park I believe, if in gear I think it locks out the override. Easiest to do it with the ignition keyswitch in run, but without the engine running in order to audibly verify the positive "click" on and back off for each of the three solenoids. If you can do it in park with the engine running, it will likely affect the idle to some extent.

KDirk

[Guest whitey]

This is a quote from above asking for Forum information about the ED20 BLM reading, when in park and closed loop. This is a '88 Reatta using the diagnostic CRT.

"The Block learn is a puzzle because it also always looks good while driving....close to 125-135 but as soon as you put the car in PARK in shows 152-155. Closed loop or open loop, always shows 152-155 immediately and stays there until you start driving again. It just wants to be rich when in PARK. Now maybe I am expecting a 128 range reading in PARK because of what I read on the FORUM and in the service manual but maybe there is some leeway here and I'm curious as to what other Reatta owners see."

[Guest whitey]

While cleaning my grounds I noticed my G100 ground stud is brassy colored. Is that normal or is that a sign of oxidation ? Also, according to above post diagram, there are 3 major negative ground junctions and the battery negative. I read in one unrelated post that there are 4 ground junctions. Am I missing one?

Edited July 3, 2012 by whitey (see edit history)

[padgett]

My 88 BLM runs high at idle and settles down when driving. I never worried about it.

Apparently you did a tuneup, did the rough idle start after you replaced the plugs ? If so and you still have a Magnavox did you gap the plugs at .060 (original spec) or .045 ? I have found the Magnavox acts a lot happier at .045 but the Delco can handle .060s.

Incidently I always use AC Rapidfires (platinum), #3 with Magnavox and #14 with Delco.

[Guest Mc_Reatta]

While cleaning my grounds I noticed my G100 ground stud is brassy colored. Is that normal or is that a sign of oxidation ? Also, according to above post diagram, there are 3 major negative ground junctions and the battery negative. I read in one unrelated post that there are 4 ground junctions. Am I missing one?

Yes, there's one on the engine by the PCV valve on the rear passenger's side.

[Guest whitey]

My 88 BLM runs high at idle and settles down when driving. I never worried about it.

Apparently you did a tuneup, did the rough idle start after you replaced the plugs ? If so and you still have a Magnavox did you gap the plugs at .060 (original spec) or .045 ? I have found the Magnavox acts a lot happier at .045 but the Delco can handle .060s.

Incidently I always use AC Rapidfires (platinum), #3 with Magnavox and #14 with Delco.

Yes, plugs were replaced a couple of months ago by the mechanic who did an overall tuneup on this newly bought car that needed a lot of work out the gate. They were standard replacements and had him gap to .045. The coil is a new Magnavox replacement (found a clearance sale for $9 a coil pack).

My question on the BLM 'rich' reading was just an attempt to see what is normal since my gas mileage can be terrible and idle can be rough. I continue to troubleshoot the weak vacuum (16") and other rough idle leads from the Forum . I may have multiple failures going on. As a target, it seems to me that if the BLM settles into a 118 to 138 range after repairs then I expect the car will be running at it best and that I have found the gremlins. If BLM 152 -155 is unusually high,which I believe it is, then I need to get it down. Thanks for your reply.

[Guest whitey]

Thanks Mc_Reatta, I missed that one. Any comment on the brassy color of the G100 stud/ground?

Edited July 4, 2012 by whitey (see edit history)

[Ronnie]

Yes, plugs were replaced a couple of months ago by the mechanic who did an overall tuneup on this newly bought car that needed a lot of work out the gate. They were standard replacements and had him gap to .045. The coil is a new Magnavox replacement (found a clearance sale for $9 a coil pack).

My question on the BLM 'rich' reading was just an attempt to see what is normal since my gas mileage can be terrible and idle can be rough. I continue to troubleshoot the weak vacuum (16") and other rough idle leads from the Forum . I may have multiple failures going on. As a target, it seems to me that if the BLM settles into a 118 to 138 range after repairs then I expect the car will be running at it best and that I have found the gremlins. If BLM 152 -155 is unusually high,which I believe it is, then I need to get it down. Thanks for your reply.

Which did you actually replace? The coil pack or the Ignition Control Module (ICM)? Or both? It's odd that you say "$9 a coil pack". It seems to mean you replaced more than one. The '88 only uses one coil pack and one ICM.

ICM on the left - Coil pack on the right on top of the ICM:

[Guest whitey]

Which did you actually replace? The coil pack or the Ignition Control Module (ICM)? Or both? It's odd that you say "$9 a coil pack". It seems to mean you replaced more than one. The '88 only uses one coil pack and one ICM.

ICM on the left - Coil pack on the right on top of the ICM:

[ATTACH=CONFIG]144402[/ATTACH][ATTACH=CONFIG]144403[/ATTACH]

I bought 2 KEM coil packs @$9 each, couldn't pass that up. I replaced my old one with the ignition coil pack (right side photo above) since there was the start of corrosion on the #1 terminal. Also replaced all spark plug wires. I do have a replacement ICM but the old one looked OK (no ooze) so I have not yet replaced that. Next on my list is to put together a backup coil/ICM package and clean the metal ground support it sits on. On this subject, is it advisable to lightly coat the cleaned ground plate with di-electric grease or just leave it bare?

Edited July 4, 2012 by whitey (see edit history)

[padgett]

BLM 155 seems normal for my 88 at idle (O2 sensor often shuts down at idle & I do not mind a bit rich then) but would expect under 135 at 25-30 mph (closer to 128 is better).

Also have not looked but would not be surprised to find the vaccuum in the 16 range at a stock 600-650 rpm idle (mine are set at 725-750 for a bit better a/c operation at stoplights.

[Guest whitey]

BLM 155 seems normal for my 88 at idle (O2 sensor often shuts down at idle & I do not mind a bit rich then) but would expect under 135 at 25-30 mph (closer to 128 is better).

Also have not looked but would not be surprised to find the vaccuum in the 16 range at a stock 600-650 rpm idle (mine are set at 725-750 for a bit better a/c operation at stoplights.

Just curious, did you adjust idle by adjusting the throttle body position sensor ? My low end voltage is .36 volts, closed loop in PARK, and seems on the low side and barely in spec. My ECM reads lean already, giving a BLM rich compensation (at idle/park only). Opening up the throttle would be the wrong direction...right? My RPM's jump around from 605-790 now. Actually I'm wondering if the TPS is going bad with that much jumping in which case a replacement would be better than an adjustment. I guess this is 3 questions.

Edited July 4, 2012 by whitey (see edit history)

[Ronnie]

I always just clean the mounting plate and install the ICM with two of the three bolts (so it will be easier to get off next time. I've never used dielectric grease for that so I can't say what the results would be.

[padgett]

First I make sure the TPS is in spec (.38-.42v at idle, over 4v WOT), can watch in the disgnostics to see if jumping.

Then adjust the speed in the programming when I also make the fans come in earlier. Have to burn a PROM for that.

Also use just 2 nuts and no special grease (just clean) for the IAC. Can rely on the studs/nuts for a positive ground, physical contact is more for cooling.

[wws944]

...Also have not looked but would not be surprised to find the vaccuum in the 16 range at a stock 600-650 rpm idle (mine are set at 725-750 for a bit better a/c operation at stoplights.

Mine measures 20 or just a tad over at idle. That is from the vapor canister port just downstream from the throttle.

Not sure what the big deal is on the third nut on the ICM. It is a little tricky to get to the third nut on if you go in from the battery side. But going in on the other side of the big connector, with ones fingers above the radiator hose, it is a piece of cake. It is probably easiest to do that nut first. Then the two easy ones.

[Guest whitey]

First I make sure the TPS is in spec (.38-.42v at idle, over 4v WOT), can watch in the disgnostics to see if jumping.

Then adjust the speed in the programming when I also make the fans come in earlier. Have to burn a PROM for that.

Also use just 2 nuts and no special grease (just clean) for the IAC. Can rely on the studs/nuts for a positive ground, physical contact is more for cooling.

Thanks, always assumed from other posts that the mounting plate was for ground, as well as mounting....but acting as a heat sink makes a lot of sense.

Let me ask you, does your G100 ground stud have a copper off color ( as opposed to the rest being silver color). I'm trying to determine if my G100 ground is being compromised by material changes in the stud over time.

Edited July 5, 2012 by whitey (see edit history)

[Guest whitey]

Mine measures 20 or just a tad over at idle. That is from the vapor canister port just downstream from the throttle.

Not sure what the big deal is on the third nut on the ICM. It is a little tricky to get to the third nut on if you go in from the battery side. But going in on the other side of the big connector, with ones fingers above the radiator hose, it is a piece of cake. It is probably easiest to do that nut first. Then the two easy ones.

That's good to know, especially where you measure your vacuum .

[2seater]

Just verified my hot idle vacuum @ 17.8"hg in park with digital gauge. I believe this will vary somewhat with your location, vis-a-vis, altitude. I am at about 720ft. I would expect it to increase with a decrease in altitude, and vice-versa. Idle is not adjusted with TPS, which is only an indicator to the ECM of the throttle position. It functions somewhat like an accelerator pump on a carburetor as well as the angle of the throttle blade. It is desirable to have it operate in the expected range.

I checked my BLM for light 30 mph cruise, which is about 122-123 and rises to 133 or so when stopped in park. This is with 24# injectors and stock PROM, so I expect it to run somewhat low. The Integrator runs in the expected range around 128, so I consider this to be normal operation. These are variable numbers, and should be expected to operate over some range. If it didn't, it would lose the self-adjusting ability.