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Fluctuating Idle

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Old 10-29-2007, 02:22 PM   #1
g8tr5220
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Default Fluctuating Idle

I have a buddy of mine in town who has a boxster, as a 996 owner I didn't have a ton of suggestions for him on the cause of this, but figured someone here might be able to offer some insight!! Maybe a vacuum problem? I had a Gen III Mazda RX-7 that did this once...

Here is his message to me:
I have another car question for you. Do you know any reason why my car (99 Boxster) would all of a sudden rev while in netural by itself between 1000 and 2000 rpm's? It will just sit there and go up and down like someone is getting on and off the gas. And when I'm in 1st and it drops to 1000 rpm's, it bucks the car like I gave it gas. Just thought I would ask you to see if maybe you knew if it was an easy fix before I brought it to a mechanic.

Thanks guys - Craig
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Old 10-29-2007, 02:55 PM   #2
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I've heard that this can be caused by a failing or dirty mass airflow sensor. However, I suggest a search on this one. I recall that uneven idle has been raised quite a bit in the past.
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Old 10-29-2007, 03:04 PM   #3
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Quote:
Originally Posted by Drew_K View Post
I've heard that this can be caused by a failing or dirty mass airflow sensor. However, I suggest a search on this one. I recall that uneven idle has been raised quite a bit in the past.
Thanks for the quick reply -
I had searched for idle issues and saw the Mass Air Flow sensor fix but it seems the MAF issues are below 1000 RPM with the car almost dieing. His issues are above the 1000 RPM mark, would that still be a dirty MAF sensor or throttle body issue?
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Old 10-29-2007, 04:06 PM   #4
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The MAF has nothing to do with the idle. MAF only affects higher RPMs. You can disconnect it and your idle won't change and you won't likely see any difference until about 4000 RPM.

The Boxster most likely has a dirty ICV (Idle Control Valve) and/or dirty throttle body.
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Old 10-29-2007, 04:16 PM   #5
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Loren

Would that be an easy DIY or should he bring it in?
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Old 10-29-2007, 11:27 PM   #6
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It is very easy. Two hex (or Torx) bolts to remove the ICV. Use some spray carb cleaner. Make sure the little paper gasket does get damaged or lost. Re-install it and see if it improves. If it doesn't hen the ICV may still be sticky and need replacement.

BTW, MY99 was the last year for non-egas cars. So, cars newer than MY99 do not have a an ICV. In those cases you need to clean the throttle butterfly.
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