This is not the crank position sensor failing at all. If you take the oil cap out and a strong vacuum is felt this is the Oil drain back valve , The valve tends to deteriate when the use of wrong motor oil is used BMW requires sythetic oil . Not regualr motor oil or a synthetic blend.The crank position sensor only picked up lean misfire due to the engine RPM speed. It would be nice to have the other "P" code, this helps determine if the Variable valve timing is at fault. The 2 item that cause this is the oil drain back deteriated or the VANOS . P1727 also means you can not acclerate to go anywhere just hold traffic up.