Suddenly idling high - 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 08-11-2010, 11:36 AM   #1
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Default Suddenly idling high

I started up my car and it idled around 2500-3000 RPM. Drove it around, and it never went below 1500. 1-2 shifting is quite awful, too.

No codes in the computer. Tested the TPS with a scantool, and that reports fine. Installed new vacuum lines two months ago.

Everything was running just fine last night. What could have changed overnight?
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Old 08-11-2010, 12:00 PM   #2
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Maybe you IAC is stuck
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Old 08-11-2010, 01:44 PM   #3
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If the IAC cleaning doesn't help. Unhook the battery for 30 minutes and reconnect. It'll need to relearn, but if there'* a technical glitch that should reset it.
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Old 08-11-2010, 02:00 PM   #4
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Quote:
Originally Posted by BillBoost37 View Post
If the IAC cleaning doesn't help. Unhook the battery for 30 minutes and reconnect. It'll need to relearn, but if there'* a technical glitch that should reset it.
I just cleaned it three weeks ago, and that cleared up my rough idle. I was careful not to spray any TB cleaner into the IAC itself, just gently cleaned the pintle until it was shiny and smooth. Still, it'* the first thing I'm checking after work.

Now, wouldn't a failed IAC valve set one of the P050x codes? I didn't even have anything pending when I scanned after a five-minute drive.
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Old 08-11-2010, 02:13 PM   #5
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Not necessarily. Depends when and which tests are run. Makes good sense though. Worth checking.
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Old 08-11-2010, 07:31 PM   #6
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Quick mid-repair status update:

Took the IAC off the throttle body, and turned the key to RUN, so I could watch for pintle movement. It didn't move at all. I turned the key back to LOCK, and then played a quick round of find the pintle. (It didn't shoot too far.)

Screwed the pintle back in, and pushed it down most of the way. Going back outside to reinstall it now. Let'* hope it works!

(The O-ring is fine, by the way.)
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Old 08-11-2010, 08:02 PM   #7
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Reinstalled the IAC, and it'* idling like it should be. How weird. The pintle moves, too.

Bill, Trixster: do either of you have an explanation? I sure don't. Regardless, I'm going to pick up a spare IAC from RockAuto just in case it happens again.
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Old 08-11-2010, 10:53 PM   #8
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If your IAC don't work your throttle body will not have the correct vac pressure to control your fuel input and your engine will run real high or low depending on where the ecm thinks your pintle is located for your idle speed. You most likely need to replace it because it sounds like the spring inside your IAC motor is going bad. Well best of luck and I am glad you found your culprit.
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Old 08-11-2010, 11:04 PM   #9
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Or your IAC gears inside your motor are so worn that it needs to be replaced and you playing around with it might of just got it working for the time being. Let us know what you find out and good luck. It is sure one easy fix though. I hope you have your new IAC installed soon and all your problems on this subject come to an end for you and your ride.
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Old 08-12-2010, 12:18 AM   #10
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I just put a brand new IAC valve on my 95 Regal before the lifter exploded and I opted for an L67 swap. If the parts are the same and you need one, I'll sell you mine cheap.
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