hello , ill do my best to try and help you get to the bottom of this . What control unit are you getting this fault ( engine or transmission ) and what is the fault code number .
thanks
i did a little more looking into the problem , the problem is probably the crankshaft sensor and a dme software issue . i would replace the sensor and if that doesn't completely fix the problem the dme ( engine control unit ) will need to have the software updated . they should charge you about an hours worth of labor at the local dealer if you tell the you need no diagnosis and only the dme reprogramed .
thanks and let me know how it works out for you
BMW Technician
12 YEAR MASTER TECH