From rough idle to high idle - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 07-02-2004, 10:10 PM   #1
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Default From rough idle to high idle

Work continues on the 93. Today'* project was removal and cleaning of the TB and boy, let me tell you, it certainly needed it. Prior to the removal, the idle was poor: rough, stumbling and stalling. Yesterday I removed the IAC only for a cleaning but after reinstallation the idle was still rough but not as bad.

The cleaning process went well. The TB was removed. MAF, IAC and TPS were removed as well. Then spray...brush...spray...brush...etc untill it looked shiny and new. The IAC received and additional cleaning as well as the MAF. I used CRC QD (quick dry) Electronic Cleaner for the MAF. Then the assembly was reinstalled.

When i fired it up, it seemed to be idling a little to high but since the motor was cold (first start of the day) I figured I'd wait for a while to let the idle kick down. Well, this never happened. It continued to idle at 1500 RPMs the whole time. I let it idle for about 10 minutes without ant change. Shut it off & started again...still idles at 1500.

I did re-use the TB gasket so I don't know if that is my problem or not. I also checked for a vacuum leak but couldn't find one. I'm not sure of the best way to check for leaks either.

Any other suggestions?
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Old 07-04-2004, 02:57 AM   #2
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Old 07-04-2004, 07:22 AM   #3
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Maybe it'* been dirty so long the PCM is trimming the IAC wrong now. Try a PCM Reset.
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Old 07-04-2004, 12:05 PM   #4
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Quote:
Originally Posted by jr's3800
Stupid question here, did you make sure to plug the TPS sensor back in?
Yea, I double checked all the connections this morning. Already I've disconnected the negative battery cable for about 10 minutes without any change. I think I'll leave it disconnected all day as we have party plans today so I won't have time to work on it anyhow. I'll post my results later.

Thanks guys.
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Old 09-06-2004, 09:35 PM   #5
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I'll dust this thread off cause I believe I solved the problem.

Taking a good look at the throttle body, I noticed two limiting screws. One for full closed and the other for full open. Just for the hell of it, I decided to try and adjust the full closed limit screw. As my luck would have it, it wouldn't budge so I got the Dremel out. I shaved a small amount of material from the end of the adjustment screw. This allowed the RPMs to go from the previous 1500-1900 to just over 1000.

I've heard that the 3800s have no mechanical idle adjustment. I'm not too sure of this after these results.

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Old 09-06-2004, 09:53 PM   #6
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Mine has a 2k rpm idle when cold, and will never go down unless the car is driven. But once its driven, BAM idle is smooth right below 1000rpm. Purrs like a kitten. Did your idle ever go down after you drove the car or whatever? before adjusting the idle screw?


-justin
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Old 09-06-2004, 10:02 PM   #7
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No, it never kicked down. It'* tough to drive the thing with no seats or gear selector :o

I've let it idle until until the fans kicked on so it wasn't a cold idle that I was experiencing. Come to think, the RPMs actually increased as it warmed.
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Old 09-06-2004, 10:10 PM   #8
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hmm.. Well, that is interesting, at least I know my problem isn't that. Good thing, I can't adjust stuff all that well. I wonder how that screw got out of wack, was it that it may have gotten adjusted while you were cleaning it? Or was the carbon build up and such so bad, that it decreased airflow so much, that hte high idle wasn't experienced at all?


-justin
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Old 09-06-2004, 10:18 PM   #9
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My guess would be your second question... kinda. The father of person I bought it from was allegedly a mechanic. After seeing all the crud on the TB I assume that the idle was becoming poor. A little twist of the screw to compensate... randman1 has a high idle after cleaning.

Just a theory.
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Old 09-06-2004, 10:33 PM   #10
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ahh, yes that does make sense. Well, at least you've got it fixed. Too bad some people don't realize the importance of cleaning up stuff, because we all know a car goes faster when its clean


-justin
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