Changed the plugs 2 months ago when I did the tune, had the car checked today and everything is fine, maybe a bad batch of OB1 or fuel was in the tank?howsit bud,
I have been running OB1 for years on many of my cars including my N54 and never had any issues, when last were your plugs changed? have you run any other additives in the past?
I hope you get it sorted soon