Volatile RPM below 3000 RPM

[nicolasboston]

Hi all

I'm new to this forum having recently purchased a 2006 bmw 130i with about 23,000 km's on the dial.

The car was running like a dream until recently. The first sign was when I had the car idling when talking to a friend outside the car. All of a sudden the car started revving itself a little, kind of like it was impatient for me to get in and drive off! I thought nothing of it as it only happened a couple of times and we thought it quite amusing.

Unfortunately the problem has worsened and occurs intermittently both when the car is idling and also when driving, usually when the engine is below 3000 rpm.

If I'm at the lights, the car will almost stall and then over-rev itself to make up for it and to avoid stalling. The needle jumps around like crazy and on some occasions will stall.

If I'm driving, say at 2000 rpm, the tachometre will jump around (feels like the engine cuts out for a few moments) and then kind of shudders and finds its feet again.

The problem is the fault is not systematic. I can start the car cold and it works fine for teh first drive, then when the car is warm (say after being at the shops) it starts to misbehave!

To date I've replaced the vanos solenoid and they have undertaken a software upgrade. Unfortunately my BMW service centre don't seem to have an answer and I want to avoid them undertaking a costly process of elimination.

Any assistance or experience people have had with this would be much appreciated. I have a video of it if anyone is interested.

[witeshark]

Are there any cracks in the plastic parts of the intake ducting?

[theluis]

check engine light?
is there any kind of hissing noise comming from intake area??
you might also try cleaning the idle air passage on the intake throtle body.

[nicolasboston]

Would this be the problem (see picture)? I noticed this yesterday having picked the car up from the service.. I can't believe they changed the vanos solenoid, changed the oil etc and missed this....

[witeshark]

I'd say that's possible.

[theluis]

if it is after the mass air flow sensor (as seen in the pic) then yes if not then it shouldnt be a problem.

[nicolasboston]

Hi guys

Thanks for your help - unfortunately that was not the issue. They have since replaced the alternator and vanos solenoid... but no love.. .apparently it is still stalling randomly.

Any other thoughts? Please help!

[brettski]

I would have gone with the vacuum leak or possibly a fuel pump/pressure issue?

[theluis]

another very serious possibility is the pcm...