Intermitent 3000 rpm idle

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  #1  
Old 04-16-08, 05:03 AM
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Intermitent 3000 rpm idle

Grand am 2001 3.4ci. I did a search and found many posts. I checked vac. hoses pcv. This first happened about two months ago. It just happened again 3 days ago and again last night. If I turn off the ign. and start it up again the idle is fine. I checked for loose connections, Where do I start TPS,IAC,ECM or Temp. sender. any thoughts Thanks.
 

Last edited by e150club; 04-16-08 at 05:26 AM.
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  #2  
Old 04-16-08, 06:43 AM
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Where do I start TPS,IAC,ECM or Temp. sender.
Actually all of the above......

Has it set a CE light.? if so , read the codes. If not likely IAC is sticking in the bore. A good thorough cleaning of the IAC port with some throttle body cleaner and a Toothbrush may help.

A bit less likely, but the TPS harness can "Loosen up" and cause this also, but expect a trouble code associated with this one.
 
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Old 04-16-08, 07:05 AM
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No CE light. I think i'll clean out the IAC to start, But would a dirty IAC rev at 3000 rpm ? I'm going to clean it anyway Thanks.
 
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Old 04-16-08, 10:42 AM
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But would a dirty IAC rev at 3000 rpm ?
It can......It is basically a needle and seat arrangement...if it gets "Gummy " enough, it can stop the IAC from seating, or retracting at all.....
 
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Old 04-16-08, 03:55 PM
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I cleaned the IAC seat and air port. I'm gonna cross my fingers. so far its OK Thanks for the replies.
 
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Old 04-18-08, 06:41 AM
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It did it again last night. This time about 2000 rpm. No CE Light. Do anyone think the IAC motor might be the prob. she turned key off and back on the idle went to norm. thanks
 
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Old 04-18-08, 12:56 PM
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http://www.xse.com/leres/efidiag/iac.html
http://www.2carpros.com/topics/iacvalve.htm
http://autorepair.about.com/cs/faqs/l/aa042603a_1.htm

under the last link, look under "surge" area. so far, consensus is that if your IAC/ISCU goes bad, it'll not keep idle right, not surge. from personal experience, i had ford taurus that had same issue, not holding idle on cold, until engine reached operating temp.

now, here comes the good part: same ISCU(idle speed control unit) almost caused a car wrack, as at some point, it decided to open throttle by itself, while i was going 65 on freeway. that was most scary feeling - car accelerates by itself, you keep pressing on brakes, and it wants to go faster.

so, i am not saying it's not your IAC. i am saying - you, probably, would have had both unstable idle and surge.

it sounds like something relevant to rpms, right? surges only at certain rpm? logically, should be something that monitors rpms? what do we have there - throttle position sensor, camshaft position sensor? as a matter of fact, i think there's a transmission module/sensor that can cause surgies, but you need someone well rounded in trannies to tell you that. whatever is dealing with monitoring spinning parts in your engine/trannie and reporting them to ECU.
 
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Old 04-18-08, 01:27 PM
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Thanks UKRKOZ for the reply: I read the last link u gave me. I will read the others later tonight. Smoke will be comming out my ears..... crank sensor humm. I'm thinking about something.
 
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Old 04-18-08, 01:36 PM
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here's how to check out your IAC

http://autorepair.about.com/cs/troub...042603a_08.htm

also says that IAC controls "idle speed only".

that was most interesting reading for me either. reason being, what i had on that taurus, is totally different. it was a solenoid type black device, sitting outside throttle body, with plunger pressing against throttle lever. it'd extend plunger to allow more air in, and retract it to allow less air in. throttle plate control, nothing like what you have in IAC. was 1987 throttle body injection 2.4L engine, i believe.
 
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Old 04-18-08, 01:40 PM
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Originally Posted by e150club View Post
Thanks UKRKOZ for the reply: I read the last link u gave me. I will read the others later tonight. Smoke will be comming out my ears..... crank sensor humm. I'm thinking about something.
u r most welcome.
i'd start with locating TPS and CPS and removing connectors/cleaning with electrical cleaner/lubricating with electrician greese. not much expense, might be nice suprise.

i am constantly tempted to say - vacuum/air leak somewhere, though.
 
  #11  
Old 04-18-08, 03:44 PM
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would probably have codes checked even if you havent never seen a check engine light it may have one stored in history that will give you an idea of where the problem is.
would suspect its probably a bad tps.
 
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