Have you installed an aftermarket charge pipe? You need to block the holes created from the removal of the stock recirculating valves. These High Temperature Vacuum caps will do the trick. Don't Run an aftermarket charge pipe with out them!
ALL N54 Equipped Vehicles, Including
2007+ BMW 335i/xi/is Coupe/Sedan/Convertible (N54 Only)
2008+ BMW 135i/1M (N54 Only)
2009+ BMW Z4 35si (N54 Only)
2008+ BMW 535i/xi (N54 Only)