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ECM/IAC - Not an ideal idle


RiggerParish
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BTW, I noticed in your video that it appears your oil pressure sender is bad because your gauge is jumping around a lot.  I doubt that has anything to do with the IAC problem but it might be worth checking out. Maybe a bad harness that goes to both of them?

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Thanks for your posts, Ronnie.

 

I replaced the ECM already, it came from a 1990 Reatta with normal idle. I was able to see the car running before the ECM was pulled. The IAC connector is looking quite rough indeed and multiple plastic parts of it missing. I tested all four wires with my meter and they tested good... but I found this IAC valve check in the manual which is the next step.

 

I hate having to pull wires out of the harnesses but this might need to be done... I will trace oil pressure sender and IAC wires. Historical evidence of mice around harness!

 

Thanks again

 

 

PXL_20201221_071651373.jpg

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Home from work. Testing can continue! I'm waiting on new wires and connectors for the IAC and TPS, both of which have seen better days.

 

On 12/21/2020 at 9:04 AM, 63viking said:

Have you run the test that is on the page you posted?. Second paragraph from the bottom.

Check the coils A&B and C&D with a voltmeter on resistants.

 

Waiting on those parts I was able to at least check the 3 IACs I have and the results (in ohms)are as follows:

 

IAC#1: A-B = 45.5, C-D = 46.2

IAC#2: A-B = 47.2, C-D = 48.0

IAC#3: A-B = 47.4, C-D = 47.4

 

A-D and B-C on all three resulted in infinite resistance. Although the tolerances (A-B, C-D) specify between 48 - 58 ....therefore none of mine really made the grade, but I think they were close enough. What were the results of your test 63viking?

 

I also performed the test light procedure (shown above) and both blue/white and green/black wires produced no lights, while the blue/black and green/white produced steady lights! Now need to check for open or short, I guess. Hope the issue is in the connector.

 

Cheers

 

 

Edited by RiggerParish (see edit history)
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  • 2 weeks later...

IAC passes testing on chart C-2 above.

 

Changed connectors on TPS and IAC, have lights on all circuits. Still idles at 1000/1100rpm. IAC 0 counts at idle so the ECM knows the idle is too high!

 

I am baffled and back to square one.

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Thanks for the reply, padgett.

 

I took the MAF sensor off to expose the butterfly valve and it appeared closed while idling. Since I am stumped and will try anything at this point, I'm going to check again.

 

Thanks again

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Every so often I take off the black tube that goes from the air filter to the throttle body and then I take an an awl and remove the ring that holds the screen in place. I then pop the screen off and use an old tooth brush and carb cleaner I spray and brush both the butterfly and the throttle body. Then replace the screen and ring and give it a try. Do the cleaning when the car is off.

You could also try cleaning the idle air control cavity [what the idle air control is mounted in]. Most people don't clean this.

Keep in mind also that there is a O ring for the MAF sensor and a gasket for the idle air control.

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4 hours ago, padgett said:

" it appeared closed while idling" Try taping on the bottom, should be completely closed. It must be getting air from somewhere.

This will be tonight's project.

 

Thanks for the reply, Dave. I've already cleaned as much of the TB as I could without taking it apart, including the butterfly. My first try at fixing this was to clean out the IAC channel and all surrounding ports with carb cleaner. The IAC o ring and MAF gasket are both present.

 

 

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On 1/8/2021 at 10:45 AM, padgett said:

" it appeared closed while idling" Try taping on the bottom, should be completely closed. It must be getting air from somewhere.

 

It appears closed and im able to stall the engine by blocking air off here. Still idles at 1000rpm.

 

Search continues.

PXL_20210110_211622990.MP.jpg

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44 minutes ago, RiggerParish said:

It appears closed and im able to stall the engine by blocking air off here. Still idles at 1000rpm.

 

41 minutes ago, padgett said:

If really completely closed, blocking off should do nothing.

Padgett I can't see how that would be possible. Air for the IAC has to come from somewhere in front of the throttle plate. I believe it comes from the square hole shown in the last photo. I would cover just the square hole and see if the engine stalls. Seems to me like if it does stall there is a problem with the IAC not seating properly, or the passageway for the IAC air is somehow allowing raw air to bypass the throttle plate and enter the engine.

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7 hours ago, TexasJohn55 said:

Another stupid question: Did it have a honeycomb screen in good condition?

 

Yes it is fine, I have attached a picture.

 

7 hours ago, 2seater said:

Agree it does not look completely closed either. I went back over this thread for the third time and I must ask; has this ever idled correctly?

 

No, it has never idled correctly as long as ive owned it. I have attached a picture where I spread some Rodico over the bottom of the butterfly valve to make sure no air was coming in and still 1000rpm. 

 

Im sorry to all if this thread is getting tedious. 

PXL_20210111_063053188.jpg

PXL_20210111_063037854.jpg

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Its after midnight and I'm still in the garage. I put some tape over what I believe is the IAC intake port. So, if the butterfly valve was completely closed, the car shouldn't start?

 

Well, the car did start and although it started at about 700rpm and settled there, it eventually crept back up to about 900/1000rpm.

 

 

 

 

PXL_20210111_083318693.jpg

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Is the car running in open loop or closed loop? And does the desired idle number change when it shifts open to closed. Also, is the AC or Defroster on? Both bump up idle request.

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It doesn’t take a lot of opening to idle. My guess is a previous owner has adjusted the mechanical idle stop, perhaps to address some other issue? Loosen the jam nut and back that little stop screw out. It just needs to keep the throttle blade from sticking in the bore.

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1 hour ago, TexasJohn55 said:

"Im sorry to all if this thread is getting tedious."

We love a mystery, hoping to learn something.

Boy Howdy, I have had super long winded threads too, and I am eternally grateful for the patience shown.😎

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4 hours ago, padgett said:

SIGH, same crack would be at top.

Sigh indeed. I should have went to bed.

 

3 hours ago, 2seater said:

It doesn’t take a lot of opening to idle. My guess is a previous owner has adjusted the mechanical idle stop, perhaps to address some other issue? Loosen the jam nut and back that little stop screw out. It just needs to keep the throttle blade from sticking in the bore.

 Located this stop screw. It does look like someone has been at it as I can see thread lock or something over it.  this looks promising.

 

1 hour ago, TexasJohn55 said:

"Im sorry to all if this thread is getting tedious."

We love a mystery, hoping to learn something.

Appreciate you saying that!

 

 

PXL_20210111_175914900.jpg

Edited by RiggerParish (see edit history)
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That throttle stop and limit screw definitely don't look right. The lower one in this view is the curb idle and does appear to be screwed in further than normal. Usually the tip is just peeking out from the casting. The upper is the wide open throttle stop and looks to be ready to fall out. Opening the throttle beyond 90* is counterproductive and I usually find full air flow slightly before 90* due to the throttle shaft. It may also over adjust the transmission throttle cable.

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6 hours ago, 2seater said:

That throttle stop and limit screw definitely don't look right. The lower one in this view is the curb idle and does appear to be screwed in further than normal. Usually the tip is just peeking out from the casting. The upper is the wide open throttle stop and looks to be ready to fall out. Opening the throttle beyond 90* is counterproductive and I usually find full air flow slightly before 90* due to the throttle shaft. It may also over adjust the transmission throttle cable.

 

They were not right! I backed the idle stop out and it immediately helped the situation. it'll fire right up at about 1000rpm and then slowly reduce to about 900/800 then when fully warmed up it drops to 700/750rpm (600 in gear). Still a touch high which I could bring down to a really nice 625rpm with the help of ES09 but this override only works in diagnostics, correct? I guess I cant just set that as my idle and it memorizes it?

 

We're getting there.

 

 

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On 12/18/2020 at 8:34 PM, Ronnie said:

 

...

 

You said you adjusted the idle and could get it down. Were you turning the screw that moves the throttle plate? If so did you adjust it back properly? It should be adjusted so the throttle plate is closed but doesn't stick closed in the throttle bore.

 

Also, you did you turn the pintel of the IAC by hand while you had it out in an effort to change the idle. If you did you could have it out of it's operating range.

 

Remember this from about a month ago?

 

 

 

Edited by Ronnie (see edit history)
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20 minutes ago, Ronnie said:

 

Remember this from about a month ago?

 

 

 

I do remember that. I was under the misapprehension that it was fully closed, in the correct position about a month ago. As you have highlighted, I am not perfect.

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1 hour ago, RiggerParish said:

I do remember that. I was under the misapprehension that it was fully closed, in the correct position about a month ago. As you have highlighted, I am not perfect.

Think nothing of it. I've been in that situation more times than I care to remember. I just hope the problem is as simple as a screw adjustment and you get you car running right. That was the goal of everyone who replied to your thread.

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Thanks, Ronnie. More often than not I miss things, but the help on here is invaluable and gets me back on track!

 

Padgett posted a helpful chart a while ago with temperatures and the idle it should be at at those temps. At 80 degrees C the idle should drop to 625 but mine is never lower than 750 unless in gear. It also idles erratically on occasion between 750-900, up and down. So still more things to iron out, just happy to be making progress.

 

Video of the new idle with ED22 displayed.

 

 

Edited by RiggerParish (see edit history)
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I don't see anything terribly out of whack on that video. I would drive it for a while and give everything a chance to sort of get to know each other before assuming the worst. It looks like to me the IAC wants it to be there. In the 700's for park/neutral and 600's in gear seems okay to me. To get absolute detail for what the ECM is shooting for, you have to get into the actual PROM to see what that particular chip was programmed for. There are subtle differences in the programming for the various chips coded for each year, maybe a little more priming shot, maybe a little change to the timing charts etc...

Kudos to you sticking with this process so it is now close to a conclusion, plus we know a lot about what didn't work too😎

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Well one thing is certain......and impressive. The owner kept at it, he didn’t give up. That is what fixes cars. No one knows everything that could possibly have been wrong on such a complicated issue. Multiple heads and countless hours of experience is what fixed it, along with tenacity. That fact that the base idle that is mechanically set was off because some tractor mechanic hacked away at the car for some reason is not surprising. The older a car is, the more likely it is suffering from two issues.........hack mechanics and short cut repairs due to cost. I have seen it countless times. Congratulations on getting the car to perform where you are happy with it. I don’t think one percent of the people who post here asking fro problems would have gotten it to its final positive outcome.

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The little bit of idle creep is probably the fuel trim switching back and forth, and over time long term fuel trim will probably stabilize the idle a bit more. A lazy O2 would also cause it to roll just a bit. Another interesting comment........the mechanically set base idle adjustment that was off would have probably been spotted by Padgett or myself in under ten minutes if actually standing in front of the car. A typed communication, and not physically being able to see in person causes a mental and visual data loss that can just about make things impossible to comprehend in a way that properly diagnoses the issue remotely.............if that makes sense.

 

Ultimately it was a vacuum leak...........just a controlled one that wasn’t properly observed. And the computer control system was ultimately fine and working properly. The car wasn’t broken..........someone “broke it” by adjusting the fixed idle. 

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4 hours ago, edinmass said:

Well one thing is certain......and impressive. The owner kept at it, he didn’t give up.

Well said Ed. I agree 100%. We have Reatta owners come to this forum all the time with problems who quickly give up and disappear. Rigger stuck with it, and with a little help he figured out his problem. I hope he sticks around for a long time.

 

Ed I'm happy to see you taking part in the Reatta forum. I read a lot of your posts in the other forums so I know you have a lot to contribute to the Reatta forum I hope you will come back often.

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