High idle 2500+

My 1996 Firebird with 3.8l is idling over 2500 rpm. I've had quite a bit of service done to it lately (118,000 miles) including dealer tuneup and transmission service, new water pump and ect sensor, new alternator, tps sensor and belt. Still idles high. Could a screwed up mass airflow sensor be the culprit? Does anyone know what it could be? Thanks.

more likely it would be a faulty IAC or vacuum leak.

usually a bad air flo sensor will make the car stall out rather than it rev high rpms on its own.

What's an IAC?

I mentioned the MAF sensor because mine appears to be cracked and I plan on replacing it anyway.

I'm reaching at this point.

Idle Air Control sensor

The Mass Air Flow sensor is probably expensive too...I wouldn't just replae it if I wasn't sure that was the problem. Have the throttle body cleaned and check out that Idle Air Control...though I think that 2500 rpms is a bit high even for a faulty or fouled IAC.

scan it for codes

The Mass Air Flow sensor is probably expensive too...I wouldn't just replae it if I wasn't sure that was the problem. Have the throttle body cleaned and check out that Idle Air Control...though I think that 2500 rpms is a bit high even for a faulty or fouled IAC.A faulty IAC valve can create any idle it wants a fully extracted and stuck IAC can cause a 4500 RPM idle and are you kidding, You think that throttle body blade being carbon funked can create a 2500 RPM idle but not a faulty IAC?. Also if the MAF sensor housing is cracked you have to replace for both performance and driveability. If its cracked its letting in un metered air and is completely throwing off your PCM from the correct a/f ratio.

If the housing is cracked and it was letting air in after the sensor it would not idle without severe coersion and throttle pedal playing. Also, I didnt figure it sounded like IAC because it sounds like it just started happening...it could be that the IAC just took a dump...also, I wasn't talking about the blades but the carbon could be affecting the IAC...I wasn't trying to undercut what you were saying LT1...just giving my 2 cents for what its worth.

If the housing is cracked and it was letting air in after the sensor it would not idle without severe coersion .
I never said that the MAF was what is causing his idle issue. I just said it requires replacement and it most certainly can be a IAC thats the point I am trying to make and carbon deposits on a IAC will raise your count higher and raise your idle but most likely its a stuck iac valve but carbon deposits on a thottle body blades would have to be the most severe I have ever heard of to cause a 2500 RPM idle.

Thats why I said that i wasn't talking about the blades. I was directing the coment about the cracked MAF to the person who posted the topic...not everything I am saying is directed at or toward you. What I was saying is that carbon can foul the IAC..."make it stick" as you said. Relax. I don't want to start a fight on an online forum over something silly. I just give my thoughts at the split second they come to mind and hope they help...my word is not god written law and I doubt anyone else's on here is. Thats the point of the forum...to have a group of opinions and hope they help solve a problem. Most of these problems are described in one sentence and could be anything...without having the vehicle in front of me, I throw what I think it could be based on what similar problem I have had in the past.

You stated a comment based on what I posted I am just replying to it. You made your opinion known and I shared why I felt it wasn't and asked if you really believed that. I don't take every comment you make like its directed towards me and if you think like that you need to read more carefully and your probably the one having a problem here not me. So lets just drop it til we find out for sure what was the cause.

As for how long its been idling high... I just bought the thing so I don't know and I've had the throttle body and fuel injectors fully serviced by a Pontiac dealer so they should be good. It doesn't always idle at 2500+ but the idle speed is erratic and is frequently high.

When I took it in the check engine light was on and so they checked for codes at that time. Came back with some cooling system problems which I am addressing.

What would be a normal idle speed anyway?

I think I want to replace the MAF sensor since it looks abused. I think I'll go ahead and replace the IAC valve also. Even if they work they are 9 years old. If that doesn't work maybe it's the computer control module or the circuits. That sounds expensive.

Thanks for the comments. I feel a lot better now having a direction to go in. I'm not a mechanic but hate to give all my money to the shops.

I replaced the MAF sensor and the IAC valve. Guess I'll drive it and see what happens.

Idle should be around 600 rpms...

I never said that the MAF was what is causing his idle issue. I just said it requires replacement and it most certainly can be a IAC thats the point I am trying to make and carbon deposits on a IAC will raise your count higher and raise your idle but most likely its a stuck iac valve but carbon deposits on a thottle body blades would have to be the most severe I have ever heard of to cause a 2500 RPM idle.

There did seem to be a fair amount of carbon built up when I replaced that IAC valve. I wiped it out with a rag.

I'll have to get my cooling issue resolved b4 I can drive it enough to see how it's gonna turn out.

Well, Good luck. Hopefully it will be a easy fix.

John

Well the idle seems to be improved but is still a little high. When the engine is cold it seems to be higher. I wonder if it would hurt anything if I pulled that IAC valve off and hit the inside of the intake with carb cleaner. I'm thinking the carbon build up inside it may be affecting it also.

The way you clean a IAC is with carb cleaner, so yes its perfectly fine to take out the sensor and use carb cleaner on it. Just be careful not to get the cleaner on the harness end and not a big whoop if you do, just make sure its dry before reinstalling the harness or I'm sure you can figure out what would happen. Good luck.
John

I removed the IAC valve and cleaned the crap out of it with carb cleaner. It's about as clean as I'm going to get it. Still has an 1100 rpm idle, which I can live with. Still, I wonder if there's anything else to be done which may bring it down to the suggested 600 rpm range. That's what my truck idles at.

Hope I'm not beating a dead horse here. I wouldn't want to end up on someone's 'You Suck' list. :biggrin:

Have you had your car scanned for codes?.
Sounds to me like its most likely a vacuum leak but there could be a couple possible other causes.

Also beating dead animals is a useless hobbie, sure its fun but what purpose does it serve?. Keep up your level of suckage and you will be on the list in no time.

I'm not beating as a hobby or for the fun of it. As a non-mechanic I must ask many questions to get to the bottom of something mechanical.

The only codes returned on my Firebird were cooling system related... so I was told by the dealer. I got that fixed. Now I'm going to explore the vacuum leak angle. Thanks for the input.

I found out I have an intake manifold gasket leak. I guess this could be part (the main part) of the idle problem also. Checking the Chilton manual I see that this is a big job and that there is an upper and lower gasket. Anyone ever replace theirs before? I was quoted $600 at a repair shop. Eeeeeee!!!

I checked the thing out with my own code scanner and got no codes.