[D1skine]

Hey, guys, I have a 2009 E93 335i N54 and recently it has had a misfire without any codes. When I start the car it is fine and idles at 600pm after the cold start, however after driving for a bit and then coming to a traffic light the idle stays around 800rpm. Under WOT and whilst driving the car is very smooth however during idle the car shakes a decent bit, I realised that when pulling the coil packs there is oil on the spark plugs so I decided to do a valve cover job and cleaned as much of the oil as possible however couldn't get all of it out. The coil packs have been changed before. However, I am confused as it only happens on idle which to me doesn't indicate an ignition problem generally so what could it be?

[PhaceN52]

Scanning for codes do you get the ones for misfires only on the oil fouled spark plug tubes? I'd start with spraying some electrical cleaner on top of the spark plugs and on the coils tips and connectors

[D1skine]

I get no codes what so ever, no rough start up either just minor shake when idling and 750ish rpms.

[lordnikon]

When you changed the valve cover did you also change the seal/gasket for the valvetronic motor?

[eljay]

Since you have just replaced the valve cover, my bet is on a vacuum leak somewhere.