It sounds like a tricky problem which I dont know much about.
If you already put on a new throttle body and still get the throttle error, that's very strange. Have you got ElsaWin? best 1st course of action is to follow the diagnostic steps as per Audi workshop manual.
I would have thought it would be easier/cheaper to do a smoke test of the whole intake system for leaks before removing and dismantling things? Your local mechanics surely know how to do this quick test?
http://www.youtube.com/watch?v=FfiQ7qWiG-M
here is the ElsaWin procedure for checking throttle valve sensors.