Weird Idle Problems

thundrburd

Registered User
My brothers sc has been having a weird Idle problem, it will rev up to about 2 grand, then drop down, and rev up, and when he puts it into reverse it jerks like it wants to take off , does anyone know what could be the cause of that, we have changed the cam sensor, he changed the iac about 4 years ago, however he never drives it, so any help would be appreciated
 
well it will stay at 2 grand when you start it, and when you put it in drive it is at about a grand, so it doesnt ever go back to normal Idle, which is my question of, does anyone know what could be wrong with it ?
 
did you try to turn the idle screw. i just use a pear of plyers and truned what looks like a stud. it might help your other wise to me it sounds like iac.
 
other wise to me it sounds like iac.
Thats the likely cause. Shouldn't need to turn the set screw... there is a port which bypasses the throttle plate to let air around it. The EEC controls the IAC valve opening and closing it rapidly to control the idle speed. :)
 
Thats the likely cause. Shouldn't need to turn the set screw... there is a port which bypasses the throttle plate to let air around it. The EEC controls the IAC valve opening and closing it rapidly to control the idle speed. :)

+1 on the IAC
 
Ok, well we changed the IAC, didnt work. Checked the adjustment screw, took off the cai and the throttle plate is closed so the screw doesnt seem to be the problem, does anyone have any other suggestions ?? when you start it, it will stay at about 1700, put it in gear and it is at about a grand. So is there anywhere else I can check that I am not thinking of ??
 
nope ask anyone else on here i think it makes higher idle . pull a vac line somewhere on the car see if it runs with a even more bad idle or gets better tell you the truth if you do so it will prob stall because it already has a bad leak.
 
Small vacuum leaks will cause a higher idle. Worse vacuum leaks will just make the motor start and die.

Did you change out the IAC with a used one or a new one? If it was used, has it been proven to work?

Otherwise, you might have a vacuum line off somewhere. Have you messed around with the intercooler tubes prior to this outcome?
 
yes, we just got done changing the power steering pump line, so we had to take of both upper and lower ic tubes, so where else would I check that could be causing a vacuum leak ?
 
What did you use to seal them up with? If you used RTV then you have to run a bead on every tube, bolt them down, and then wait for them to dry for an hour or two.

That is the cause if anything.
 
well it doesnt appear that it is leaking anywhere around the ic tubes, so does anyone else know what it could be ? could the tps sensor cause the high idle ? he unpluged it and there was no change in idle, so does that mean its bad ?
 
im also trying to diagnose an idle problem. ive changed the TPS and IAC and still have the same problem. im almost 100% convinced that its a vacuum leak or somewhere in the SC tubing theres a leak. spray carb cleaner around all your vacuum lines while its running. if u hit the leak with it. rpms should kick up.
 
When i unpluged my tps befor my car stalled. you can use a mutimeter and look somewhen on the forums on how to check it . i forget what it should be.
 
tps voltage is measures from the black wire and orange wire. voltage should be between .95-.99v at closed throttle. and about 5v at WOT. u check it with the key in "on" position but engine off.
 
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