Only thing I can contribute is:

VW's & Audi's (same difference) are NOTORIOUS for having 'Check Engine' problems-any good mechanic will tell you that. That being said, this is an known engineering problem with these cars. The PCM in them is generally always at fault and it isn't a matter of IF it'll happen but when. Try this is you don't believe me...search CL for any VW or Audi product (Again-they're the same vehicle). Call and ask the prospective seller if the light is on. They will say "yes".
The sad and expensive thing about this is the 1st thing people do is throw good money after bad. I know you may not want to hear this but you be best served by selling it. Buy a boring Toyota. You'll quickly forget what a Check Engine light even was!

Power Train Control Module....sorry, that's a Ford term, but what I meant was whatever Audi calls it.