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  #1  
Old 09-30-2012, 08:33 PM
Matt W Matt W is offline
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Location: Scottsdale
 
Join Date: Sep 2012
Posts: 3
Mein Auto: E39
Am I Correctly Diagnosing my 'Hunt for Idle' Problem? - ICV or Computer or Other?

Hi -

I want to be certain that I have properly diagnosed my problem - I hope you can help - thank you for taking a look.

I had a 'hunt for idle' problem with my '03 530i.

Suspecting the Idle Control Valve, I removed it, cleaned it, lubricated it and replaced it.

Though to a lesser degree, the problem still exists.

Are these ICVs robust enough that a good cleaning does the trick or is their failure mode revealed by what I am describing? Is it time to replace the valve?

If not the valve itself, what about the computer? Is there a way to test the computer / control part of the ICV operation? Does this have a reputation for failure?

I have not cleaned the MAF sensor because 1. it looked pristine and 2. I didn't have any MAF sensor cleaner on hand and 3. I have been told that a dirty MAF would not be a leading cause of the symptoms I am observing.

Thank you very much for any insight you can offer.

Matt
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  #2  
Old 10-01-2012, 02:53 AM
Andrew*Debbie's Avatar
Andrew*Debbie Andrew*Debbie is offline
resU deretsigeR
Location: Anglesey
 
Join Date: Jul 2004
Posts: 6,252
Mein Auto: Leaf Tekna
It is probably not the DME (computer).


Might be worth looking for vacuum leaks. How old is your O2 sensor?
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The models and equipment (standard and optional) illustrated in this post reflect my misunderstanding of vehicles supplied by BMW AG to the German market. In other EU member states, the truthyness of my posts may vary. Please ignore this post. Subject to change.
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Old 10-01-2012, 07:48 AM
Matt W Matt W is offline
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Location: Scottsdale
 
Join Date: Sep 2012
Posts: 3
Mein Auto: E39
Thank you.

The oxygen sensors were replaced at 120k when I bought the car a year ago. It now has 140K.

Just to clarify ...

The engine RPMs are perfectly sinusoidal. The frequency is approximately one Hz and the amplitude of the engine speed variation is about 500 RPM - ranging from 1000 to 1500 RPM. On rare occasions, when sitting at a long light, the frequency will creep to increase by about 50% and the amplitude will grow to approximately 1000 RPM (1000 to 2000 RPM).

The onset of these symptoms correlates to nothing - engine temperature, air temperature or humidity, driving conditions - nothing. In fact, shutting the car off and immediately restarting it always solves the problem. It can recur as soon as the next traffic light or not until the next day.

I wanted to clarify the behavior of the engine more accurately since I later realized that 'hunt' could have implied an irregular or sporadic symptom.

Thank you again for weighing in on this.

Matt
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