idling problems on 350i

[neiloconnor]

Hi, Can anyone help?

I'm looking for the most likely cause of this problem on my 3501. When the car is warm I have trouble keeping the engine running when I have to come to a quick halt. The car drives as normal when moving, but when I stop, unless I have my foot immidiately back on the throttle, the revs fall too low & the engine dies. It allways restarts first time, but will not idle. This only happens after the car has been going for about 15-20 minutes.

Thanks in advance.

[D1 MAD]

Greetings and welcome to the forum.

Have you set your tick over to start with when the engine is at normal working temperature? I had a problem with mine a while back, I would set it and then after a few miles would have to set it again. Cured it with a small drop of thread lock at the side of the adjusting screw, not enough to seize it up but enough to stop the screw vibrating loose.

[chedder]

Could be a weak tension spring on the 'flapper' MAF unit, hard braking would cause the flap to move forward and upset the through airflow.
It may be possible to adjust it with the screw for the CO settings.

[ed_crouch]

I know its my hobbyhorse, but...

it could be the ignition amp on its way out.

Mine id exactly this. Would idle OK cold, but when it warmed up the idle went to rats. Still went OK, but no idle.

Ed.

[SimonV8ster]

Why has nobody mentioned the stepper motor ?? I thought that this sounds like classic syptoms of the stepper motor being dirty ??

[ed_crouch]

i think we all assumed it to be a flapper. if its hotwire then you are spot on, and this is defo possible.

ed.

[ferlin]

Lots of ideas here but I would try adjusting the mixture screw first before getting too technical

[neiloconnor]

My thoughts were also on the lines of stepper motor problems, But I changed my mind when this only happened when the engine was warmed up. Wouls this not happen when cold if it was the stepper motor?

[Wedg1e]

neiloconnor said:

My thoughts were also on the lines of stepper motor problems, But I changed my mind when this only happened when the engine was warmed up. Wouls this not happen when cold if it was the stepper motor?

The stepper is properly called the 'Idle Stabilisation Valve' because that's what it does, not just when cold. Under ECU control it acts to feed a metered amount of air into the plenum to keep the idle speed more or less correct. When it sticks (and it will) it gets the correction wrong and strange things happen.