My 2004 5 spd Cooper with 72K is starting to bogg down with what feels like either a missfire or a fuel delivery issue. When I take off or am below 3000RPM under load the car boggs down & seems to miss. This also happens if I punch it at low RPM. Does anyone have any thoughts on it? The plugs are supposed to have another 30K on them and I don't want to replace them if it isn't needed. I really don't want to talk to the Mini dealer about it because they won't tell me anything except "We will have to fix it!" & I would rather not have them work on it.