Engine Idleing High!

Ok i own a 2000 alero 3.4 with 90000 miles on it. For a while now i've been having a problem with my engine quite often. The engine stay's at 2k - 4k RPMs while sitting still at a redlight or when the car is in park. It is very difficult for me to be able to hold the brake pedal down while this is happening. While the car is in Drive the RPM's are much lower (of course), this can be anywhere from 1,200-2,300RPM's. when the car is shifted into neutrel, the RPM's go way up to around 4K.

Now this problem is not consistent at all, sometimes happens a few times thoughout the day... and sometimes not for a week or 2. This problem is really starting to show wear on other parts of the car (extra stress on brakes... Been though 2 sets of rotors, beatin on my third).

Any ideas what could be causing this? Thanks!!

[K Dan]

bad IAC or vacuum leak can do that. but since it isn't happening all the time I'd rule out a vacum leak. so it might be a bad IAC (idle air control), you could try cleaning it.

What exactly is an IAC? Where is it? and how would i go about cleaning it?

Maybe your throttle cable is stuck open a bit too much. wasnt there a TSB on some cars because of that?

[K Dan]

I'm not exactly sure where the IAC is on a 3400 (i guess i could go out and look) but it's gotta be near the throttle body. It's a valvle that lets air in when the throttle is closed so it can idle . You could just use brake or carb cleaner to clean it. To see if it's the cable with the car running (while it's idleing high), open the hood and see close the throttle any by hand.

I'll play with it this weekend and see what I can come up with. Thanks for the tips guys, I'll let ya know how it goes

I had the same problems two days ago ITs kinda scary cause it makes breaking hard and you have to put the car in park then shut it off quick so it doesn't rev up on you at first i thought its was my new cams but i found out it was sumthing to do with my ported throttle body, so i took out the IAC sensor cleaned out the port put a new oil ring on it put a little bit of motor oil on then bolted that down tight. Next i zip tiped down all the hoses going to my throttle body to make sure there were no vacum leaks cause that can cause a high idle too then I retightend down my throttle body. Next turn your car to then on postion let it sit for 10 secs turn it back to off for ten seconds then turn the car on. Your suposed to do this while the car is cold then let it idle up to full tempreture. That whole key sequence thing i told you to do makes your IAC readjust and start over. Since then ive had no problems. I did all that stuff to make sure i coverd all areas but im pretty sure if i had just did the IAC stuff that would have fixed it. And hope your IAC ain't bad there between 60 and 80 to get new. Hope All this helps!

Mine used to do that, if you ahve a Haynes Manual and test the Throttle Position Sensor(TPS). I replaced mine and it worked wonders. Hope I was some help

Well guys... I took that sensor out and cleaned it up really well using carb cleaner. The whole thing was covered in soot. Immeditly after putting it back in, the car was running much better!! One of those "episodes" has not reoccured yet (its only been a few days) but from the vast improvment with the normal engine idleing, I feel that this did the trick. Thanks a ton!!!