ERRATIC rev counter PLEASE HELP
 

Hello all. i have an audi a3 2.0 tdi sport and the rev counter jumps erratically on idle and throughout the rev range, on watching the needle it is not noticabe when the engine is cold but when it is at running temp it will jump up and down like mad, its been to audi and they could not fix it, any ideas welcome please help as its doing my head in... thankyou...