Check the crankcase ventilation piping, it could be oil/water blow off if the connection on the bottom of the intake plenum is disconnected.
I had that smell when the oil catch can I was using was hooked up wrong, the stuff smells TERRIBLE! Oil/Gas nastiness...
2001 M3, LSB 6spd, purchased 6/09 with 25K miles.
Mods: Coyne Performance built ///M3