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[rgowers56]

this problem is occasional and makes the car have idle that rises and falls upon starting,driving,restarting after driving if i rev the engine i get black smoke out of the tailpipe with a heavy smell of unburnt gasoline after holding the idle at 1500rpm the problem abates and the vehicle goes back to running normally i have replaced the fuel pressure regulator the one that was in the car was 3.0 bar the replacement is 2.5 bar please note that these problems do not happen under consistent conditions they occur seemingly at random times any help or knowledge would be greatly appreciated

[edjack]

There is a valve that controls bypass air, and thus, idle speed. It may be sticky. On the M30, it resides under the intake manifold, about in the center of the block. I suspect yours is in the same place.
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Ed BMW CCA member since 1987 (Nr. 62319).
'97 540i 6 speed Aspensilber over Aubergine interior.

[rgowers56]

thanks ed this possibility was considered but discounted as the flap works well the problem ended up being the coolant temperature/negative temperature switch it was the original one and the brass studs that hold the prongs on had loosened and built up dirt till proper connection was not occuring upon replacement the problem dissappeared completely once again thank you for your response rob g in pittsburgh