It doesn't take much oil from the air filter to fowl up the MAF, this is a known issue when using a K & N air filter. Use a good quality electronics spray cleaner, from radio shack, to clean the MAF, it has a very sensitive internals. If cleaning doesn't help you may need to replace it.

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/ / / Mike
BMW X5 Xdrive50i 2015 F15
BMW 325iC 1992 E30
BMW X5 4.4i - sold
BMW 335i X Drive 2010 - sold
BMW Z4 3.0is 2006 - sold
BMW 325is 1993 - sold
BMW 2002 1976 - sold

X5 Garage