In Reply to: Idle problem (miss or small backfire) with 95 M3 posted by Melby on March 09, 1999 at 16:54:59:
It seems to me that the valve cover gasket was the only influencing thing that was touched. If it was not put on properly, a small leak *might* affect the amount of air that goes into your cylinders, causing it to run rich. To compensate for this, the computer would lean the engine out. However, if the gasket leak is minute, the air pressure can fluctuate, and basically the computer will hunt for the appropriate fuel amount. At higher rpms, the air pressure (due to the vacuum effect of the cylinders) stabilizes, and thus the best timing becomes closer to the calculated timing.
In my opinion, the gasket was not put on right. It seems to me from all the info you gave, that the only thing that they screwed around with that could have affected the idle is the gasket. Make them re-replace it for free. Contact BMW if you have to. They did a crappy job is your excuse, and since new parts are covered by warranty (1 year) they are obligated to fix it for free.
If you're lucky, you would also get your money back for the air-mass sensor because of their incompetence and misdiagnosis.