Originally Posted by FIRST1
I'm not sure if everyone knows this already... If your still under maintenance/warranty, you get a free spark plug replacement at 45K... Ask your SA
EDIT: That may be for N54 only. Not positive.
New plugs are covered for both N54 and N55 at 45K miles.
The OP's problem could be ANYTHING!!! He should have his fault memory read for codes thrown. IF now codes were thrown... I would look for a boost leak.