Very high idle
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Joined: Jun 2010
Posts: 97
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From: Potomac MD
Very high idle
1986 Vette L89.
The problem I am having is the really high idle. When I first start it up it sits around 8-900rpms. After a little bit of driving it gets to the point where if I dont even give it any gas with my right foot it will bring the car up to about 40mph. When I come to a stop it feels like I am holding on the brakes and trying to accelerate at the same time. It sucks.
If I come to a stop and shift out of drive into neutral it will rev up to about 2000-2200 rpms without touching the gas pedle at idle. Then of course when I put it in drive it jumps into gear and is ot a very nice ddrop into gear. I am afraid if I keep this up the tranny is not going to like me.
Anyways I am thinking that this is due to some vaccuum leak. I took off all the emmissions stuff like the air pump and such. Where do I start and how do I diagnose?
Thanks!
The problem I am having is the really high idle. When I first start it up it sits around 8-900rpms. After a little bit of driving it gets to the point where if I dont even give it any gas with my right foot it will bring the car up to about 40mph. When I come to a stop it feels like I am holding on the brakes and trying to accelerate at the same time. It sucks.
If I come to a stop and shift out of drive into neutral it will rev up to about 2000-2200 rpms without touching the gas pedle at idle. Then of course when I put it in drive it jumps into gear and is ot a very nice ddrop into gear. I am afraid if I keep this up the tranny is not going to like me.
Anyways I am thinking that this is due to some vaccuum leak. I took off all the emmissions stuff like the air pump and such. Where do I start and how do I diagnose?
Thanks!
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
I'd probably use unlit propane to see if you can find the leak. Failing IAC can also cause that.
Burning Brakes
Joined: Nov 2010
Posts: 1,006
Likes: 2
From: Spartanburg South Carolina
Whens the last time you've cleaned your Throttle Body? Might give that a shot also. I just cleaned mine the other day and it was horrendous. could also be the ICV like he mentioned ^ how many miles are on the car?
Drifting
Joined: Jun 2010
Posts: 1,853
Likes: 8
From: Westerly RI
The fact that the idle is more or less normal at cold start would lead me to suspect something other than a vacuum leak. On cold start, the ECM is in "open loop" and ignores voltages from the IAC, TPS, etc. and uses default values. When the car warms up, the ECM goes to "closed loop" and uses inputs from the various sensors.
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
The fact that the idle is more or less normal at cold start would lead me to suspect something other than a vacuum leak. On cold start, the ECM is in "open loop" and ignores voltages from the IAC, TPS, etc. and uses default values. When the car warms up, the ECM goes to "closed loop" and uses inputs from the various sensors.
If you had a USB <==> ALDL cable, you could download TunerPro or TunerCat and see what was going on. Not sure if a scanner can do that.
Makes me wonder if you can remove/plug the IAC to see what it does (after warm-up).
