i think its your crankshaft position sensor.on RealOEM it is listed as "pulse generator - crankshaft". Any shop you go to would refer to it as a crank position sensor. Here it is on RealOEM:
http://www.realoem.com/bmw/showparts...58&hg=11&fg=10 It's #14 on that illustration. Part #12141247622
my friends car had what seems to be the same problem and it got fixed.
just a suggestion im no mechanic though... hope it helps