my 05 does it as well, only after idleing a couple minutes. Dealership checked it out under cpo warranty and said nothing was plugged or clogged, no codes, no problem. Yet they saw how bad it smokes after ideling then reving. They told me it was an engine problem requiring a tear down. I would be responsible to pay if nothing was found broken, cpo doesn't pay for worn parts. Their advice was 'drive it like you stold it'.
Halifax BMW terrible.
Most of the threads on here say the problem was valve seals. Some were fixed under cpo, thats burns hearing that. Halifax bmw sucks imo.