rough idle only in drive - 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 12-25-2002, 01:17 AM   #1
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Default rough idle only in drive

at first when i got the car it would idle in drive just as smooth as in park or neutral know it has a rough idle on when your at a complete stop the car will vibrate it idiles at 900 rpm when i put the car into neutral you cant feel a dam thing it idles like it should it cant be the fuel filter because wouldt it idle rough in park or neutral as well ive put in some fuel treatment hasnt really made a difference what is it i do notice that if while in drive with one foot on the brake if i push just slightly on the gas w/ the other the rough idle smooths out but thats only because it raises the rpms slightly more but im already at 900-1000 rpm what hte hell should i do
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Old 12-25-2002, 05:37 AM   #2
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I had a similar problem. Are you losing any coolant? Mine was the intake gasket on driver side rear. didn't lose much but as it got worse it would miss under load (going up a hill). I did the work myself and it took the better part of a day to complete. But for the 50 or 60 bucks I spent the time was worth it. Oh by the way mine is a 94 with 215000 miles. all in all it has been a great car. Let me know what you find I hope I could be of some help.
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Old 12-26-2002, 12:54 AM   #3
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I've got the same idling problem with my '95 Bonneville! I don't have power loss problems and recently had the cooling system checked out, everything seems fine. Idles at 900 RPM and it shakes you to death! Yet in park or neutral or driving, it is fine.
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Old 12-26-2002, 09:58 PM   #4
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It is almost definietly the Idle Air control valve. Mine is screwed up in my car and it does the same thing.

It could also be a software problem but I know that can't be the case in my car since the computer is only a year old.
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Old 12-29-2002, 03:04 AM   #5
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Yikes! How much did that set you back?

I'm starting to get disgruntled with my car... problem with idling and some problem with the rear air shocks. Bah!
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Old 12-29-2002, 03:39 AM   #6
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Ok, my Mom has a 93 LeSabre. Had the same problem. Idle in park or neutral was fine. We went after the fuel filter and fuel dryer thinking it was bad gas. Didn't do a thing. Felt like it was hesitating under load.

I talked them into plugs and wires. Plugs fixed the problem by about 50%. They're doing wires very soon. My plugs were supposed to be gapped at .060" (yours too) and mine were eroded to .090 when I changed them. I had a similar problem. Try it. They probably need to be changed soon, anyway, if not now.
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Old 12-29-2002, 04:02 AM   #7
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Thanks Will. Gee, that sure sound better than the PCM!!! In my last tuneup, they replaced the plugs and said the wires were fine. They were probably wrong. Time to put in AC Delco wires!
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Old 12-29-2002, 04:37 AM   #8
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Don't bet the bank on it, but do it anyway for good measure. They need it by age alone, and it'll rule one more thing out. Keep us posted. I do recommend ordering Taylor 8mm wires from Hector rather than AC Delco. Taylors are much better.
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Old 01-04-2003, 01:59 PM   #9
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ok, the idle air control valve(IAC) it a controlled vac. leak that the pcm uses to control the idle speed. the pcm tires to keep the idle at a certain rpm , no matter whatt is causing it to come down. if you put it in gear, it will drop for a sec then come back up. turn the air on and it does the same, as well as turning the steering wheel. the IAC is on the side of the TB. take it off and use cleanner to get the carbon off of it. then use a senor safe cleanner to clean the seat in the TB where it sits. when you put it back together, it may take a little to get started because of the cleanner that you sprayed in the TB. once it idles, let it learn the idle again , then put it in gear and wait 60 secs. then turn the air on and do the same. then drive it and see if it goes away
hope this helped a little.
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