Thread: UPDATE > High Idle - problem solved - IAC Valve ( Intake Air Control Valve )

2001 Pontiac GP - 3100.

I need some help here.
It's scary to drive this thing, need this fixed ASAP.
In Park and Neutral, my RPM goes up to 3900 and sits there. Happens right at start up and RPMs never go down even when engine is hot.
In Drive it goes down to 1800 and sits there.
In Drive, if I let go of the brakes - the car takes off like a bat, due to unusually high RPM.
When I drive this car, my foot is constantly on the BRAKES! .. not good at all.

WTH is the matter with this thing?
Is it an idle issue?
A vacuum issue?
Something else?
Please help.

id start with a huge ass vac leak.( find and fix that) maybe try cleaning the TB. the butter fly flap could be sticking also.

I was thinking vacuum leak too, but the idle doesn't fluctuate - just stays there. So can it still be a vacuum leak?

I am not entirely sure how the cruise control is routed on that, but it could be something to do with it being stuck there. I had a similar issue on my Stealth once.

Originally Posted by hitman92499

Could still be big vacuum leak. Or throttle sticking open...or IAC sticking. Lots of fun things.

What could be the source of this big vacuum leak? I just don't see how a simple loose or torn vacuum hose could cause this. What specific vacuum areas what I need to look into?

any time un metered air get into the engine the rmps can go up or down to a stall, all depends on where the vac leak is.

the 3100 is notorious for vac leaks too.

The reason a vacuum leak can cause this is it is letting in air that the TB is not. The throttle body restricts incoming air to the engine. If you took the throttle body off and started the car the engine would rev til it hit its limiter.

Where can I find a vacuum diagram for my '01 3100 ?

you dont really need one, just follow all the small vac tubes around the engine, look for cracks or one broken off completely.

also take your air filter tube off the TB make sure the flap is closed at idle.

Originally Posted by hitman92499

Figured since you were close by, you might want to swing down for diag, but it's all good.

Thanks for your help man. I just don't know if it's safe to drive on my brakes, I don't feel too comfortable driving more than 5 minutes like this. I'll let you know though, thanks.

Will I get a Check Engine Light for a faulty IAC valve ?

it should. if your cel is on have the car scanned.

no CELs. I'm hunting blind here. Thanks for the help guys. If anyone can add to this, please do. Any guidance is appreciated.

check all that has been listed, thats all you can do for now.

I have found that sometimes you do, and sometimes you don't get a service engine light with ANY sensor when it goes bad, so the light not being on doesn't rule out anything. Definitely start with the vacuum lines and check the throttle body and idle air control as suggested. Something is allowing too much air in.