High idle and revving?

Tiny
JSC21583
  • 2003 PONTIAC GRAND AM
  • 80 MILES

I have a 2003 Pontiac Grand Am 3.4 liter. Sometimes the engine starts revving high uncontrollably. It doesn't happen all the time, but when it does happen, it does it sometimes when I start the car, or when i'm driving down the road, or when i'm sitting at a stop light. I tried replacing the idle air control valve and the throttle positioning sensor, but it still does it. Any ideas?

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Sunday, September 4th, 2011 AT 5:46 PM

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Tiny
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Did you clean the throttle-body? Any applicable trouble codes? How high do the rpms go? Maybe a vacuum leak? If it happens at idle in park, block off the mouth of the throttle body, see if any effect on the idle, should be a big effect. If no effect, you have false air getting in there from somewhere.

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Sunday, September 4th, 2011 AT 6:58 PM
Tiny
JSC21583
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It's actually my fiance's car. Her dad said he cleaned the throttle body. I scanned the car with a OBD-II scanner and it said no trouble codes. Someone told me it could be a computer problem and I may need to have the computer reflashed (whatever that means?) I've listened to it while it was running at idle and I don't hear any vaccume leak but I could be wrong.

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Sunday, September 4th, 2011 AT 7:46 PM
Tiny
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Yeah, if the problem is intermittent, it can be a pain to track down. Can you put a scanner on it that shows live engine data?

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Sunday, September 4th, 2011 AT 8:05 PM
Tiny
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Are you losing engine coolant or engine oil? Might be an issue with lower intake gasket?

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Sunday, September 4th, 2011 AT 8:10 PM
Tiny
JSC21583
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I think there might be a leak in the lower intake gasket because I found a little oily residue in the reservoir a while back. I have since flushed the coolant, but obviously that wouldn't solve the problem of the gasket leak. How would the lower intake gasket leaking affect the idling?

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Sunday, September 4th, 2011 AT 8:20 PM
Tiny
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It may cause a vacuum leak. Vacuum leaks can effect your idle. I can't see much from here, I can only make suggestions.

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Sunday, September 4th, 2011 AT 8:26 PM
Tiny
JSC21583
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Yeah that actually makes sense. Vacuum leak=erratic idle. Thanks for the suggestions, appreciate it! Repaired the lower intake gasket, didn't work.

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Sunday, September 4th, 2011 AT 8:45 PM
Tiny
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Put a scanner on it, that shows live engine data. Look at idle and idle required, they should be close to the same. You can also look to see if anything is being commanded ON, like the ac. Also, I'd have to look at sensor signals, to see if anything doesn't look right?

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Wednesday, September 7th, 2011 AT 2:14 PM
Tiny
JSC21583
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I hooked up a scanner to it last night, and it had 2 codes:

-EGR valve flow low input
-evaporative emission purge flow fault

Last night after her dad and I replaced the intake gaskets, she drove the car home and she had to hold the brake just to keep it from taking off on her. The car idles at between 1500 and 2500 RPMs and if you put it in drive and let off the brake, it'll get up to about 40-45 mph on its own. I followed behind her on the way home and she was riding the brake practically the whole time. At first it happened every so often, put lately its been happening more and more frequently. It seems like the last week or so, it happens almost every time she turns the car on. A few nights ago, she left to go to work, and she tried to start the car 3 times, and it started up, idled all crazy, and then it shut off on her. She couldn't keep it running. I don't wanna keep throwing money at it, but i'm running out of ideas.

Someone also told me it could be the mass air flow sensor?
At this point i'm shooting in the dark.

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Wednesday, September 7th, 2011 AT 2:40 PM
Tiny
2CARPROS KEN
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Hey JSC21583,

I would service the mass air flow sensor becasue this is what it does when it is dirty.

Also check the air intake boot for tears, this will fool the maf and cause stalling and low power.

Here is a guide to help you.

https://www.2carpros.com/articles/mass-air-flow-service

and

https://www.2carpros.com/articles/how-to-replace-a-mass-air-flow-sensor-maf

and

https://www.2carpros.com/articles/replace-an-air-intake-boot

Please let us know happens so it will help others.

Best, Ken

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Thursday, December 15th, 2016 AT 5:25 PM

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