i have a 2000 sunfire 2.4 5 speed and when i am driving I go to slow down or put it in neutral the RPMs stay at what ever they were say 3000 for example and wont come down till i make a complete stop and even then it only goes down to 1600 and it normally idles at 900 i cleaned the iac off and i don't see any vac leaks.
does any one have an idea of what is causing this problem?

listening...have a 96' and it does the same sometimes


"sometimes the respect is more important..."

I have an '02 Z24 and had a high idle problem. this is what I did:

1. checked the IAT and TPS to make sure they weren't faulty. I basically swapped them out for known good units from a friend's 2.4, and no change.
2. my buddy sprayed WD-40 around the intake manifold and injectors while the motor was running. the motor bogged down a bit, so that told us that there was a leak in the area.
3. I replaced the intake manifold gasket. while I was at it, I took my TB off, took all the sensors out, and cleaned it. no change however.
4. I bought the injector o-rings. pulled the fuel rail off, pulled the injectors out, and gave them a good cleaning. after they were dry, I re-installed them, using the new o-rings. no change there either.
5. out of pure frustration, I unhooked my battery for about 15 minutes. I hooked it back up, and bam... idled perfect.

why the PCM set the idle high, I have no idea, but it worked. also gave me a chance to clean up the TB, intake and injectors too.


Desert Tuners

“When you come across a big kettle of crazy, it’s best not to stir it.”

Don't overlook the simple answers either- sticking throttle plate being the first. could be a weak throttle return spring or a dirty TB. get under the hood, rev the engine and see if it sticks from there. that would be my first test.




I may not be the sharpest crayon in the box, but at least I'm a pretty color

Cleaning the throttle body and IAC valve should resolve this for you. Keep in mind after cleaning these parts, when you start your car, it may take a few minutes for any excess solvent to be consumed in the motor and your car may seem like it is running on 2 or 3 cylinders for a minute or two, also the motor may rev a lot initially as the IAC valve adjusts to it's proper position in the throttle body. From my experience, you may get away with cleaning the IAC valve a couple of times before it requires replacement. Don't forget to use some oil on the o-ring (to keep it from cracking) and some oil on the moving parts of the valve to prevent it from sticking.
After a day or so, should your car continue to idle high, try this :

When you get the car to idle at a reasonable level, 1000 rpms + /- , remove the electrical plug on the IAC valve and then test your car out and see the difference. This will help you narrow down as to what part is actually causing the problem (IAC or throttle position sensor).
It worked for me. My car hasn't run better and I think I may wait a few days or longer before I fork over $110 for a new IAC valve.

99 Cavalier Z24 5 speed
291,000 KM

from what you said it seems to the the Idle Air Control Valve. but before you go replacing that first check the throttle plate to see if its sticking and opening all the way. the way you do it is take the intake tubing off of the throttle have a buddy get in the car (with the car off) and press the gas pedal to see if the throttle opens and closes freely. if the throttle plate is good then most likely it is your IAC valve. Im not to sure where it is located on the 2.4 models but on the 2.2/2200 it is on the back of the throttle body. Once you find the IAC remove it and before you go buying a new valve, first clean it thoroughly because sometimes you can get away without having to replace it by cleaning it. if the idle is still high after the cleaning you need a new iac valve.

The IAC is on the front of the throttle body on a 2.4 Litre motor, located very close to the throttle cable.

"i have a 2000 sunfire 2.4 5 speed and when i am driving I go to slow down or put it in neutral the RPMs stay at what ever they were say 3000 for example and wont come down till i make a complete stop and even then it only goes down to 1600 and it normally idles at 900 i cleaned the iac off and i don't see any vac leaks.
does any one have an idea of what is causing this problem?"



Ok I took the car to my friends shop last night we used a snap on scanner to scan the computer and it says there is a map sensor problem so we went down and got another one off another car (He owns a auto wreckers) and it did the same thing so either this is not the problem or both sensors are bad. When we unplugged the map the rpms came back down but it ran real ruff. The other thing we noticed is that the computer was reading the tps at 25% with the throttle closed 24% if you really push on it. If it wasn’t for this I would just go buy another map but is the tps reading write or would a map or tps cause my problem any info would help

Thanks

I had the same problem with the Subaru and it was a vacuum line

ya we checked for vac leaks but did not find any pretty sure it either the tps or the map anyone else have any thoughts about my last post above.

"i have a 2000 sunfire 2.4 5 speed and when i am driving I go to slow down or put it in neutral the RPMs stay at what ever they were say 3000 for example and wont come down till i make a complete stop and even then it only goes down to 1600 and it normally idles at 900 i cleaned the iac off and i don't see any vac leaks.
does any one have an idea of what is causing this problem?"


My car was doing the exact some thing l last week until I unplugged the electrical connector on the IAC valve when it was idling normal (@1000 rpm + or -).
Now my car runs perfect. The motor on your IAC is probably weak - to confirm, try what I did. You have nothing to loose.

when i unplug the the electrical connector on the IAC valve th RPM climb to 5000rpm very fast and at that point i turn the engine off