I've read about and seen videos of direct injection engines (other brands) with dirty air intake manifolds and cylinder head ports, causing loss of power and efficiency, with costly cylinder head rebuilds. Much of the dirt comes from PCV gasses entering the intake. Since the fuel/air mixture does not pass through any internal passages, the solvent properties of the gasoline can not maintain a clean, smooth surface. I've been able to clean the intakes on other cars I've owned (without direct injection) by removing the flexible intake tube between the mass airflow sensor and the air filter box, spraying Gumout or intake cleaner while someone revs the engine. Today I removed the air intake from the air filter box on the M6, and was surprised to see anoter filter, mostly a fine metal mesh, embedded into the top of the air cleaner box (fits over the air filter). I tried to pry it out, no luck. Has anyone had any problems with dirt and PCV crud building up inside the intake manifold and intake ports in the head? My car has 119,000 miles, with no performance, fuel economy or driveability issues. I'll leave it alone for now, but want to prevent future problems if possible.