Had issues for some time with this
Started with a slight grating sound and lots of smoke when accelerating with severe power being unleashed

played with all the vacuum pipes and checked the MAF sensor, if you disconnect this all seems well (back to normal) apart from the engine management light on, cleaned this with carb cleaner (just the same)

However broke down last week, got towed home and had a look at the EGR valve, the valve inside the EGR was broken off, took it off and got a new one from Audi for 220 still the same !!!

I have now made a crude blanking plate to blank the exhaust gasses from entering the inlet manifold, again this seems to get me going and the car can now drive

Any ideas any one

Lynd