Hi ive just done a 500 mile round trip in my 01, a4 2.5 tdi quattro i noticed halfway through the journey it was down on power on the motorway, but once i came off at a slip road and stopped the engine is vibrating and feels like it only running on 5 cylinders you can feel it through the floor and steering wheel, theres no engine smoke atall, no odd noise's its just running roughly, Ive only had the car 2 days, and i was really starting to love it!. Has anyone got any ideas or tips that i can try out to solve the problem?? any help would be much appreciated