audi a6 3.0 tdi injector

got a a6 55 plate 3.0 tdi got a misfire on 1 cylinder no one can test the injectors there the bosch .....115 injector.you increase the revs by 20/50 rpm it goes or put the aircon on.took it back to where i brought it from and its been in a garage now for 3 weeks now its at audi stil no joy, no codes coming up. i keep telling them its the injector tip its not spraying the fuel properly and or its dripping does anyone no how to find out which 1 it could be or shine any light on this i'm getting XXXX with audi

audi are now replaceing the throttle body as if that will stop the injector from leaking !!!!!! what a laugh

finally got the car back today!!!!!!!!!!!!!!! still not right engine now judders when braking just on the brink as you stop and a little bit on tick over no smoke though!!! the new 6 injectors have stopped that o well looks like its going back in again