hi I hope someone could shed some light on a situation I have with my audi, last night on my way home as I was accelerating, the car started to judder!! only while accelerating, and also I have noticed today that every time I accelerate a cloud of black smoke comes out the exhaust, the engine is sounding rough too! I have asked the advice of a few ppl only to be told different things, I would like to see if anyone else has had this problem and if so what it could be and how much it is likely go to be to repair? plz help.