1993 idle problem
Thread Starter
Burning Brakes
Joined: Mar 2005
Posts: 800
Likes: 2
1993 idle problem
My 1993 LT1 doesn't idle consistently. When you start it dead cold it won't idle at all, just stalls out. Once it has run for a minute or two it was idle, very low (tach is below 500 rpm and it sounds like it is struggling to run). after the car warms up it idle's too high (tach stays around 1000-1200). If the car is warmed up and you start it it will idle at 650ish like it's supposed to but after you let it run, without touching the throttle the RPM's creep up to around 1000-1200.
I have replaced the IAC, found a broke wire going to the IAC so with that repaired I set the idle per the FSM, slightly depress accelerator when the car fires let go of throttle and run for 10 seconds, shut off for 5 and restart. i have checked for vacuum leaks all around intake manifold and there are none. i have checked all vacuum hoses, all the way to the firewall, no leaks anywhere.
Does anyone have any idea's as to where to go now?
I have replaced the IAC, found a broke wire going to the IAC so with that repaired I set the idle per the FSM, slightly depress accelerator when the car fires let go of throttle and run for 10 seconds, shut off for 5 and restart. i have checked for vacuum leaks all around intake manifold and there are none. i have checked all vacuum hoses, all the way to the firewall, no leaks anywhere.
Does anyone have any idea's as to where to go now?
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
If you had an L98 I would tell you to do a "minimum idle adjustment". I assume there is a similar adjustment for LT1s, but I don't know that.
Usually idle wandering around is caused by a vacuum leak...
Usually idle wandering around is caused by a vacuum leak...
Thread Starter
Burning Brakes
Joined: Mar 2005
Posts: 800
Likes: 2
But would a vacuum leak cause to not idle cold and idle fast hot? I don't have a way to measure iac counts. But when you turn the a/c on the rpms don't move, so at least I know the iac is working.
Advanced
Joined: Aug 2013
Posts: 71
Likes: 2
From: Oregon
I had a bad vac leak on my 93 LT1 last summer, You could sit in the car at a stop light and hear it sucking air into the intake.
Even when I fixed it the idle only changed a small amount.
I dont think its a Vacume issue.
I am trying to rack my mind to come up with other ideas though...
A smarter then me buddy on LT1 says, its your IAC is cloged or not working correctly or you need to relearn your Idle.
Also if you mess with the idle screw then you will need a tech tool from a dealer to properly reset the idle when you find the cause.
Even when I fixed it the idle only changed a small amount.
I dont think its a Vacume issue.
I am trying to rack my mind to come up with other ideas though...
A smarter then me buddy on LT1 says, its your IAC is cloged or not working correctly or you need to relearn your Idle.
Also if you mess with the idle screw then you will need a tech tool from a dealer to properly reset the idle when you find the cause.
Melting Slicks
Joined: Mar 2008
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From: Delta B.C. Canada
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FWIW, the idle problem on my 92 was caused by gremlins in the ECM. I had it rebuilt and no problems since.
