This Audi has failed the MOT emission test because once the engine is hot it becomes impossible to hold the engine revs at the correct speed. As you press the pedal the revs increase upto 1200 rpm at which point they shoot up to 4200 rpm. When you back off they instantly drop off to just above idle.
It came to me with a dirty throttlebody and a few split breather hoses. After these repairs I reinitialized the throttlebody, roadtested and rechecked.
It generates no fault codes, drives very well, the emisions at idle are spot on. I can find no air leaks or faults with the engine condition, engine management, ignition or emissions.
I remember some Fiats suffering from a similar problem which was a software issue. Before I give up and refer the customer to the dealer has anyone any previous experience with this fault?