The 2007-2016 Audi S8 4.0TFSI and 5.2FSI direct injection engines are subject to carbon buildup in the intake system which can cause power loss, OBD codes and a check engine light , and a rough idle . In normal engines, the engine is cleaned by the gasoline flowing through the injectors and into the intake system, however, the S8 uses direct injection so gasoline does not flow through common carbon buildup areas.
Possible trouble codes include: P0300 , P0301 , P0302 , P0303 , P0304 , P0305 , P0306 , P0307 , P0308 , P0309, P0310.
The solution is to remove the intake manifold and professionally clean the intake manifold, intake ports on the cylinder head, and the intake valves. This may need to be done in as few as 20,000 miles.