Idle control problems


New Member
May 25, 2001
My car's idle seems to jump around. When I start it, it idles fine, where its suppose to. Then I will drive around, 20mins later the idle will be around 1400, goes up 400rpm. Then 10mins later it will be back to normal, 1000rpm? Would a bad brake boost cause this?
The brake booster is definately a possibility.

First thing I would do is watch the laptop to see what your IAC is doing. If your IAC is all opening up (causing the high idle), you might want to check the temp vs. idle speed graph for starters.

Assuming that the IAC is all the way closed and the idle is still too high, then the next thing I would go for is a vacuum leak. Since the idle seems to be inconsistent, I would suspect a worn-out (but not quite broken) part- the brake booster is a great example. Get one of those hand-help vacuum pumps and see if the booster will hold vacuum- if not, there's our culprit.

Other than that it could be a leaky vacuum hose (with cracked rubber, so that when it's bent "just right" it leaks, and when it bends the other way it seals up) etc. A bit of detective work should tell you.

Somehow or another, air is getting into the motor- you just have to find where.

-Bob Cunningham
found my problem, my throttle blade screw came loose not allowing the blade to retract. This also explains why my dyno run was only with a 75% tps