small miss/Rough idle when warm.... - 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 12-08-2010, 01:24 PM   #1
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Exclamation small miss/Rough idle when warm....

98 SSEI 315xxx kms

when car has been driven for awhile and has reached full operating temp it will idle a little rough every 15-45 seconds not bad enough to stall........... sounds like small misfire but not big enough to through codes any ideas??

new plugs wires new coil packs cleaned injectors cleaned intake/maf
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Old 12-08-2010, 01:40 PM   #2
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Check your fuel pressure, could be a slow fuel pump or fuel filter. But seeing it does it hot that'* a long shot. I would pull the throttle body and clean it. Also check the PCV and EGR. EGR is a good possibility because it happens when it'* hot.
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Old 12-08-2010, 01:45 PM   #3
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throttle body has been cleaned pvc is good and egr is clean...........I will try fuel filter nxt

maybe CPS?
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Old 12-08-2010, 01:55 PM   #4
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Don't see that causing a rough idle. Hot also has me think coil or ICM.
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Old 12-08-2010, 02:06 PM   #5
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hmm ok good to know!
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Old 12-08-2010, 02:50 PM   #6
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When testing the coil (there'* a write up in techinfo/testing) try testing with the coils both hot and cold. Warm up a bit in the oven and test. then put in the freezer and test again. Compare the readings. I've seen many coils test good, only to start failing when hot.
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Old 12-09-2010, 01:14 PM   #7
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its got to be ICM I guess, I changed coil packs though
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Old 12-09-2010, 01:15 PM   #8
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it only idles rough for a few seconds like a small missfire than its fine again.......
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Old 12-09-2010, 07:29 PM   #9
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My bonneville does the same thing, no codes. Its like it stumbles. I've tried replacing quite a few components to no avail.
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Old 12-09-2010, 07:46 PM   #10
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Ya I hear ya I think its a common thing for these 3.8 series 2 motors was thing about replace Cam Positioning Sensor next but Im kinda lazy and its not the ezest sensor to change
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