W124 idling from cold intermittent problem

[mika]

The following occurs intermittently , say , 1 in 5 times
it only occurs from cold and lasts for just a minute maximum
it is apparent during stop start driving but undetectable when on the move
On start up from cold the revs rise and fall from approx 700rpm to 1000rpm
no problem when in P or neutral but a little invasive when in D
The car starts as soon as the key is turned and runs very well generally

Any thoughts ?

 

[Charles Morgan]

They all do it but to different extents. My 320 would rev up on start up (more when cold) then it would settle to a normal revs after a minute or so. When at 1000 ish moving off was hairy if tightly parked.