[QUOTE]are you sure your k&n has the same quality of filtration as a stock filter?[/QUOTE] There have been quite a few cases documented on the MB forums of MAS sensors giving up soon after the fitting of K&N filters. Apparently, the MAS sensor gets fouled up. As most german cars use the same manufacturer for these kind of parts (Bosch) I suspect than BMWs would also be prone to problems.