coilpack, turbo seals, or headgasket.. unlikely to be anything else..check side of the head fpr weeping by the afm, its a tell tale sign of headgasket failre, check the coilpack for cracks. and gets someone to stand behind it , when you rev it or follow you and see what colour smoke you have.. grey/black is unburnt fuel, anything else is trouble, but varying degress of. you dont want blue.white.. but tis always difficult to tel from in the car.