Car revving up and down by itself when engine is warm

1998 BMW 523
Avatar
SERDISS
  • MEMBER
  • 7 POSTS
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
Jul 27, 2012 at 6:59 PM
Advertisement
Avatar
ASEMASTER6371
  • CERTIFIED EXPERT
  • 52,796 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
Jul 27, 2012 at 7:07 PM
Avatar
SERDISS
  • MEMBER
  • 7 POSTS
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?
Jul 27, 2012 at 7:21 PM
Advertisement
Avatar
ASEMASTER6371
  • CERTIFIED EXPERT
  • 52,796 POSTS
nope, it needs to be verified by a scanner. expensive guess.

Roy
Jul 27, 2012 at 7:32 PM
Avatar
SERDISS
  • MEMBER
  • 7 POSTS
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?
Jul 27, 2012 at 7:37 PM
Avatar
ASEMASTER6371
  • CERTIFIED EXPERT
  • 52,796 POSTS
could be mass air flow, o2 sensor, coolant sensor. i would not guess at this as it is expensive andmost likely wrong.

Roy
Jul 27, 2012 at 7:49 PM
Avatar
SERDISS
  • MEMBER
  • 7 POSTS
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!
Jul 27, 2012 at 7:57 PM
Avatar
ASEMASTER6371
  • CERTIFIED EXPERT
  • 52,796 POSTS
all sensors are temp sensitive

Roy
Jul 27, 2012 at 7:59 PM
Avatar
SERDISS
  • MEMBER
  • 7 POSTS
Alright thanks a lot! I will replace the ICV and see if it fixes the problem. thanks for your time!
Jul 27, 2012 at 8:05 PM
Avatar
ASEMASTER6371
  • CERTIFIED EXPERT
  • 52,796 POSTS
good luck
Jul 27, 2012 at 8:08 PM
Avatar
SERDISS
  • MEMBER
  • 7 POSTS
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!
Jul 27, 2012 at 8:08 PM
Avatar
ASEMASTER6371
  • CERTIFIED EXPERT
  • 52,796 POSTS
it can leak vacuum and cause this condition

Roy
Jul 27, 2012 at 8:28 PM
Avatar
SERDISS
  • MEMBER
  • 7 POSTS
Thanks!
Jul 27, 2012 at 8:35 PM
Avatar
BLONDU IONUT
  • MEMBER
  • 1 POST
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 £
Any idea?
Apr 11, 2017 at 1:22 PM
Avatar
STRAILER
  • CERTIFIED EXPERT
  • 53,854 POSTS
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
Apr 15, 2017 at 12:05 PM