Interesting, I came across a number of threads regarding problems with carbon buildup / carbon deposits and the cars throwing CEL codes for misfires. Some cars reporting losing as much as 20-30hp. It turns out that the FSI technology VW/Audi is using has a flaw.
Basically, because the fuel is sprayed directly into the combustion chamber, the valves accumulate dirt from the blow-by oils, etc and cause a buildup of carbon deposits. Some fixes have required replacing the valves. For others, it’s been to remove the intake manifold and use solvents and shell blasting the valves as needed (as early as 6000 miles).
http://forums.audiworld.com/showthread.php?t=2745246
http://forums.audiworld.com/showthread.php?t=2746852
http://forums.audiworld.com/showthread.php?t=2745791
http://www.bobistheoilguy.com/forums...Number=1414263