rough idle

[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?

[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.

[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.

[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.

[whitey]

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

[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:

[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:

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?

[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.

[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.

[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.

[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.

[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.

[whitey]

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.

I sit at 1200 ft. so that may be part of what I'm seeing for vacuum. I am replacing the fuel pressure regulator and EGR gaskets this weekend. The FPR was not leaking but since my fuel pump rubber seals were totally disintegrating I expect the FPR diaphram to follow. One thing is apparent, seals that sit in gasoline and in the 100F + heat for extended periods go bad first. After this, replacing all the underhood vacuum lines will be the last thing left to do unless my ECM/MEM-CAL/connectors are faulty. I'm working on a back up. When I get done I will have a great parts car. Thanks for the update, it helps me know what is normal.

[whitey]

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.

Replaced the FPR and EGR sensor but there was no improvement in the rough idle. Got some vacuum increase when I replaced the rubber grommet in the valve cover but still have rough idle . While searching for more vacuum leaks noticed that the fuel vapor canister's tank supply hose was looking weathered/ discolored so I will replace that when the part arrives. I have a question about the fuel vapor canister.....are you supposed to see a filter in the bottom of the canister when looking up into the air hole from underneath the car? I'm accustomed to seeing the filter at the bottom but I don't see anything there. If I should be able to see it then I have none and my canister is probably very dirty. Which leads to this next question... Does replacing the filter and removing the canister require pulling out the washer bottle or will it wiggle out once the 2 top canister bracket screws are removed?

[whitey]

Thought I would wrap this up with some positive results. The rough idle is no longer. It was cause by a combination of problems. The fuel pump was going bad, the TPS was worn and needing replacement, the ICM was overheating and starting to cook the green. These things along with a couple of fixed minor vacuum leaks has it running like new. This car has only 32K miles on it but this shows that a lot can go wrong when they sit in hot storage. A sincere thank you for all the help. I could not have done it without you.

[Machiner 55]

Whitey,

I have a question about the fuel vapor canister..... are you supposed to see a filter in the bottom of the canister when looking up into the air hole from underneath the car? I'm accustomed to seeing the filter at the bottom but I don't see anything there.

There is, for lack of a better term, a false bottom inside the canister. So, when looking up into the hole at the bottom that is what you'll see. Not the bottom of the filter, whether it has one in it or not.

John F.