Compared to the AC Delco filter, the K&N“plugged up” nearly 3 times faster, passed 18 times more dirt and captured 37% less dirt....
http://www.nicoclub.com/archives/kn-vs-oem-filter.html
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If no codes are being thrown use Chevron Techron fuel injector cleaner (concentrate). It solves rpm fluctuating upon cold start-up. Also, for most BMW problems start off by scanning your car with the Peake Research Tool. It contains the actual BMW codes. If you want to register a newly installed battery for free (just buy a $10 cable) and google/download BMWLogger