Surging revs m104

[aka$h]

The revs when in idle initally surge from 500-1500rpm, and settle down after 30 seconds and will then only be between 500-700rpm. This is with a brand new MAS, prior to changing it the problem was not as bad, it did not surge so high initially but the problem was still present.
I very much doubt its a faulty MAS, I did try the old one on again and the revs do still surge but only form 500-700. I think this may be as the new sensor is giving a more accurate reading, but the underlying is problem is still present.
Anyone had similar problems?
Cheers

 

[aka$h]

Just searched back to one of my older threads,

Another common problem on the M104 engine is the infamous engine surge they can suffer from....especially noticable when the engine is fully warmed up with the car in gear but stationary....the engine starts surging and the car rocks back and forth against the brakes. This is caused by a dirty throttle body, which is rarely cleaned during servicing. The resulting crud that builds up on the butterfly flap in the throttle body creates an air leak which then causes over fuelling/confusion at the ECU.

 

[MDMB69]

It could also be the throttle acuator. Very expensive part. I sorted out my slight surging by cleaning the throttle body but my cruise control still surges, I changed or tested everyting and narrowed it down to the throttle acutator. I stripped it down and the wire insulation inside is all broken on lots of the wires, when I have the time I might re-wire it, new re-man part is about £450 from bba-remanufacturing. OE part form stealers is about £900 I think.

 

[Vlad]

9 times out of 10 its a dirty throttle body.....doesn't cost anything to clean and very easy to do.

If that fails....there's a device on the passenger side inner wing which has two tubes going into it and has MOT printed on the top. This item can get clogged with carbon which can also effect the engine by way of surging. Its a push fit, so very easy to replace and costs about £50

Good luck.