The same thing happens to my E39. The answer I received was that it was probably due to a leak in one of the hoses. I had it checked twice and it was not the problem. I never followed up with it. Car idle still fluctuates on cold start and sometimes stalls when left to warm up. I hope you have more luck than me in getting the answer. I will check back.
You mean you do not see the problem once the car is warm? My e46 99 328 does it once in a while too, particularly in cold weather. I asked Mike Miller, he thought it was the Idle Control Motor problem. I am thinking of changing it soon, the part is not very expensive, but getting to it is a pain. Well now it is not as cold and my problem does not appear as regular. I may put off a while.
If you are experiencing an idle "dip" (idle drops to ~ 450 rpm then increases to over 1200 rpm and smooths out for a few seconds) without a check engine light I would put a bet on it being a software issue. This is a somewhat common problem on the older ms42 dme. The fix would be letting your dealer program the dme, or go ahead and purchase some aftermarket software (eg Shark Injector) and do it yourself. Of course if you have lean mixture or air mass faults those should be addressed first.
my problem does not exist only when it is cold out. It occurs year round when first starting the car in the morning. It seems I need to take a trip to the dealer to check computer chip.
