ive been having this ongoing problem with my car, it has ended up having a new boost valve, air flow meter and turbo! its a 170 a4 sline quattro. it ended up being the inlet manifold flap actuator diaphragm valve (something like that!)
now the surprise......... i asked C+R (who i trust and rate their work) how much they would supply and fit the part, they said around £400 and i had the same answer from a VW/ Audi specialist in Kings Lynn around £400! i asked Audi Kings Lynn more for a laugh than anything else, and they quoted £237.16 inc £65 for diagnostics, double take!!!
had the work and the car is so much better no more hesitation around 2k rpm