Mechanics

CAR REVVING UP AND DOWN BY ITSELF WHEN ENGINE IS WARM

1998 BMW 523

Hello,
I have a 1998 BMW E39 523i that has recently started revving up and down by itself, sometimes to very high rpm. It only does this when the engine is warm, never on a cold start. I've read it could be the idle control valve or the mass airflow sensor, however I don't know how to find out exactly what the problem is. Any advice/solution is greatly appreciated!
Thanks
Avatar
Serdiss
July 27, 2012.




There is a idle control valve that could be the failure but checking it requires a scan tool.

Look for vacuum hoses off first before proceeding.

Is the check engine light on?

Roy

ASEMaster6371
Jul 27, 2012.
Thanks for your response. The check engine light is not on, and as far as I can see, none of the hoses are in a bad condition. Are there any signs to a faulty idle control valve?

Tiny
Serdiss
Jul 27, 2012.
Nope, it needs to be verified by a scanner. Expensive guess.

Roy

ASEMaster6371
Jul 27, 2012.
Well, if it's the most likely cause of the problem it might be worth replacing it instead of having it checked out at a garage. Are there any other sensors (or any part at all) that could cause this problem?

Tiny
Serdiss
Jul 27, 2012.
Could be mass air flow, o2 sensor, coolant sensor. I would not guess at this as it is expensive andmost likely wrong.

Roy

ASEMaster6371
Jul 27, 2012.
Alright. I will check all the hoses again. Why would the problem only start once the engine warms up? Thanks a lot for your time!

Tiny
Serdiss
Jul 27, 2012.
All sensors are temp sensitive

Roy
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ASEMaster6371
Jul 27, 2012.
Alright thanks a lot! I will replace the ICV and see if it fixes the problem. Thanks for your time!

Tiny
Serdiss
Jul 27, 2012.
Good luck

ASEMaster6371
Jul 27, 2012.
Ah, one more question. Isn't the idle control valve only supposed to work when the car is idle? The car also revvs up and down randomly while accelerating (apart from when you floor it). So shouldn't an ICV malfuntion only happen when the car is idle?
Thanks!

Tiny
Serdiss
Jul 27, 2012.

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