1997 Audi A4 2.8 Quattro, tip. Just gt my car back after a cam belt change and at idle it feels as though one cylinder is missing. Also under 2000 revs while driving there is a vibration, again as if it is missing. Once above 2000 revs the car behaves as before, being smooth and responsive. Does anybody have an idea what could be wrong? Is it a case of having the garage replace the belt or is it somthing simpler?