High Idle 1990 3.1

[elca69]

I'm having high idle problems with my 3.1 automatic.It just started idling at 2,000 rpms.It runs fine...just idles high.Can't find any codes that has set.Any clues would be greatly appreciated.

[elca69]

Does anybody have ANY ideas ?????? Thanks

[denisond3]

I dont have a Cavalier, but I think they use an Idle Air Control Valve to adjust the idle speed, like all the other fuel injected cars. The IACV eventually will get sticky or stuck, usually when the car has gone well past its first 100k miles. So that would be one thing I would suspect. Also, if there is a vacuum leak letting too much air into the intake manifold, the computer would compensate (when it sees a lean mixture at the exhaust oxygen sensor), by increasing the amount of fuel. So look for a vacuum leak, even a PCV valve that has stuck in the bypass position. You could try plugging the various vacuum lines one at a time, to see if any of them brought the idle down.
Another possibility would be that the throttle valve is not fully closing. They can get enough dirt built up around and behind them that it prevents the valve from closing properly. So try twisting the throttle valve shut by hand and see if it helps.
Although its rare, a torn diaphragm in the vacuum brake booster is impossible to see, but will let a lot of air into the intake manifold. It might not be a large enough rip to affect how much brake 'boost' you feel under your foot.