'00 Alero - fast idle - a few things already tried.

G'morning all...

My fiance's '00 Alero 2.4L. 70k miles.

A couple of months ago it started with this fast idle problem.

*Cold Startup - engine rev's to ~3k, then levels out at ~1800. When warm it'll drop to a steady 1200 rpm idle.
*Warm startup - engine rev's to ~3k then falls right to 1200 rpm.
*In park/neutral - the car idles @ 1200.
*In drive with load (on the brakes) the car idles ~1k.

No CES or SVS lights / codes now.

So far I have replaced the TPS (had a code), replaced both O2 sensors (had a code), replaced the IAValve, checked the IAC (resistance constant on both sides), cleaned out the throttle body with 1/3 can of spray, and checked plugs/boots/coil.

Still, the car runs high all the time. Her gas mileage has dropped to ~15mpg avg (used to be ~20-22), because the engine is always under extra load.

I'm out of ideas. I've had an independant shop look at it (~1 mo. ago) and all they found was the TPS fault.

Thanks for ANY help.

-Nick

It is possible that the TPS is not properly adjusted and causing the issue. You may also want to clean the mass airflow sensor as it can cause a high idle condition. Also check all the vacuum hoses for a leak. A cracked vacuum line can cause a real idle problem and they are sometimes very hard to find.

Good Luck!

The idle problem was present before the TPS was replaced. You think it may have simply gone out of whack?

I'll try to chase the vac lines this weekend.

It is possible that it may be a bad one or it may just need to be properly set. Most of the newer designs don't need any adjustments but sometimes they can go out of adjustment. I will bet you will find a vacuum issue that is causing this problem. You have replaced practically everything else.