idle problems

[John Robertson]

My wifes 740 turbo suddenly revs up quickly then settles down to a sweet
idle .It does its rarely ,but you wouldn't want to be behind a car at the
lights when it happens .Any clues please?I have cleaned the air idle mixture
unit out as it was messy but this is a different problem .It revs quick and
fast then returns calmly at around 800 rpm .

 

[zencraps]

Sounds like an intermittent short in the wiring harness leading to the
constant idle speed motor. Replace the wiring harness.