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Car revving up and down by itself when engine is warm

Tiny
SERDISS
  • MEMBER
  • 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
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Friday, July 27th, 2012 AT 6:59 PM

14 Replies

Tiny
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  • MECHANIC
  • 52,797 POSTS
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
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Friday, July 27th, 2012 AT 7:07 PM
Tiny
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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?
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Friday, July 27th, 2012 AT 7:21 PM
Tiny
ASEMASTER6371
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Nope, it needs to be verified by a scanner. Expensive guess.

Roy
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Friday, July 27th, 2012 AT 7:32 PM
Tiny
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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?
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Friday, July 27th, 2012 AT 7:37 PM
Tiny
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Could be mass air flow, o2 sensor, coolant sensor. I would not guess at this as it is expensive andmost likely wrong.

Roy
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Friday, July 27th, 2012 AT 7:49 PM
Tiny
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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!
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Friday, July 27th, 2012 AT 7:57 PM
Tiny
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All sensors are temp sensitive

Roy
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Friday, July 27th, 2012 AT 7:59 PM
Tiny
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Alright thanks a lot! I will replace the ICV and see if it fixes the problem. Thanks for your time!
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Friday, July 27th, 2012 AT 8:05 PM
Tiny
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Good luck
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Friday, July 27th, 2012 AT 8:08 PM
Tiny
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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!
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Friday, July 27th, 2012 AT 8:08 PM
Tiny
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It can leak vacuum and cause this condition

Roy
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Friday, July 27th, 2012 AT 8:28 PM
Tiny
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Thanks!
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Friday, July 27th, 2012 AT 8:35 PM
Tiny
BLONDU IONUT
  • MEMBER
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Hi I have kind of the same prob
I have a 523i e60 from 2007
And when I first start the engine on cold the car rev it self a bit obove 1000-1500 and goes back to normal but in the same time the car judders for a couple of sec.
What can it be? I been to bmw and they told me I need to change all 6 fuel injectors but thats 2100 Â
Any idea?
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Tuesday, April 11th, 2017 AT 1:22 PM
Tiny
KEN L
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It sounds more like it can be a vacuum leak or a MAF that needs replacement, here are tow guides that can help you get the problem fixed.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

and

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

Please run this test and get back to us so we can continue helping you.

Best, Ken
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Saturday, April 15th, 2017 AT 12:05 PM

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