I have a k&n in my car and it works fine. Got mine on amazon for $45.
2009 AW 535i
-Sport, Premium Package, and Comfort Access
-20" Forgestar F14 Black Gloss, Cobb PTF E30 map, KW V2 CO's, Remus Sport Exhaust, BMS DCI, RPI Scoop, Full Front 3M PPF, 35% tint all-around, Orion V4's, Bruce v6.1L cables, LED interior lights, WeissLicht License Plate LED, Trinity Smoked LED side markers, Bimmian Smoked Reflectors, OEM black gloss grills, and Invisibulb turn bulbs.