Filter may have something to do with it. It also doesn't filter very well, but that is a side issue.

Could also be MAF sensor, 02 sensors, coils, plugs, or a vacuum leak. I would start by looking for a vacuum leak, that is the cheapest, and it could affect both banks.

__________________
2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue