From my understanding you can watch the cobb YouTube video or one on their site (http://www.cobbtuning.com/BMW-335i-xi-i-xDrive-s/1200.htm) you should be able to log your car with your cobb and look for a misfire. The video is for replacing.
Just a suggestion before going through the disassembly.
[font="Comic Sans MS"]e90 LCI
Cobb: Stg1 +FMIC Aggressive ST
VRSF 7" FMIC - Next To Do: White Rings
"If you're not 1st, you're last" -Ricky Bobby