High Idle when engine warm - bad IAC??
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TECH Enthusiast
Joined: May 2008
Posts: 537
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High Idle when engine warm - bad IAC?? First, I have run many searches here and elsewhere but can't seem to find a similar issue.
1999 Z28, all stock engine and tune. Car is a DD with about 150K miles. Reliable, 26 or more mpg, only issue is intermittent high idle when engine is warm, typically on a hot day. Has happened 3 times in last 2 months.
I suspect the IAC is gummed up but wanted some opinions before taking anything apart. No codes on scan, other than idle car appears to run fine. As mpg is same as historical, I am guessing MAR and O2 sensors are OK. As it does not happen all the time, not sure it would be a vacuum leak either.
Any advice appreciated. Probably going to pull it apart this weekend regardless.
1999 Z28, all stock engine and tune. Car is a DD with about 150K miles. Reliable, 26 or more mpg, only issue is intermittent high idle when engine is warm, typically on a hot day. Has happened 3 times in last 2 months.
I suspect the IAC is gummed up but wanted some opinions before taking anything apart. No codes on scan, other than idle car appears to run fine. As mpg is same as historical, I am guessing MAR and O2 sensors are OK. As it does not happen all the time, not sure it would be a vacuum leak either.
Any advice appreciated. Probably going to pull it apart this weekend regardless.
I had an intermittent high idle situation recently and it turned out to be a bad tps sensor in my case. I was able to see that the tps wasn't resetting to zero like it should when it was hot through efilive. Car ran fine otherwise.
In your case I'd check the simple stuff first. Clean up the maf and the throttle body.
In your case I'd check the simple stuff first. Clean up the maf and the throttle body.
TECH Junkie
Joined: Nov 2013
Posts: 3,913
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From: White Bear, Mn
I had an intermittent high idle situation recently and it turned out to be a bad tps sensor in my case. I was able to see that the tps wasn't resetting to zero like it should when it was hot through efilive. Car ran fine otherwise.
In your case I'd check the simple stuff first. Clean up the maf and the throttle body.
In your case I'd check the simple stuff first. Clean up the maf and the throttle body.
12 Second Club
Joined: Sep 2005
Posts: 4,273
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From: Bucks County, Pa.
The o-ring/gasket for where the EGR pipe goes into the top of the intake manifold is also notorious for shifting, and getting mangled, thereby causing a vacuum leak as well.
I seem to have to replace mine every half year or so, but they are very cheap on Rock Auto (~$1.10 each for the Victor Reinz/Mahle brand).
I seem to have to replace mine every half year or so, but they are very cheap on Rock Auto (~$1.10 each for the Victor Reinz/Mahle brand).
