Rough idle around 1000 - Update 1/16/08, Wasn't PCM. - Page 2 - 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 12-14-2007, 02:23 PM   #11
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Ok, did some diagnosing today.

1. Removing the brake booster line and capping it did not make any changes.
2. No vacuum leaks present, checked. Plus the idle was rough before me and petraman even touched the engine when he owned it.
3. No awkward noises except for the belt squeak I have.
4. On another note, when I do go WOT sometimes, I get a awkward smell out of the exhaust. Really can't explain the smell, but I am being told that the smell is normal on forced inducted cars when going WOT.
5. Should I pull my belts off for a few seconds and see if the idle changes?

Any help would be great, the roughness to it drives me nuts as it shakes everything in the car. :(
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Old 12-14-2007, 05:59 PM   #12
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Did you clean the IAC and passages? Is the MAF screen removed?
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Old 12-14-2007, 06:12 PM   #13
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IAC and passages were cleaned when the SC was off, and MAF screen is present.
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Old 12-27-2007, 10:14 PM   #14
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Little update. Lately it has seemed to ever so slightly smooth out, and idles at about 975-980 now. I still have the "unstable" idle though. I was being told that my IAC may be going bad, but I am absolutely sure that a bad IAC will only cause a high or low idle, not rough. Needless to say, I am afraid to spray starting fluid around certain areas to find a vacuum leak. And this is coming from a kid that used to play with starting fluid torches.
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Old 12-27-2007, 10:19 PM   #15
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Try a Seafoam treatment, it can't hurt.
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Old 12-27-2007, 10:21 PM   #16
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It was done in June when I got the car.

I think the first order of business is pulling the plugs, I am going to check the gap on them.
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Old 12-28-2007, 03:43 PM   #17
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Hmm, well the plugs are fine. No odd discoloration, gap was correct. I am gonna check for vacuum leaks though, just to rule it out.
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Old 12-28-2007, 08:07 PM   #18
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This may be way out there...or totally irrelevant.... but could it be the MAF sensor? Mine went bad and monkeyed up the idle and it ran rough while driving. It didn't make it idle high, but that doesn't mean it couldn't. MAF'* are expensive and require a special star scredriving to take off. If you could try one (from another good-running car), it would be interesting to know if it makes a difference.
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Old 12-28-2007, 08:15 PM   #19
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Well....... you just may be on to something. I never really check to see if it was the MAF, but it'* very possible. What readings should I be seeing on the scantool?
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Old 12-28-2007, 08:31 PM   #20
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I never really mentioned this, but I do also have hard starting when first starting in the mornings, sometimes it happens, sometimes it doesn't. Fuel pressure is in spec also.
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