BMW, Audi and VW direct injection engines (2.0FSI and TSI and BMW 135/335/535 model engines) currently have carbon buildup issues on their valves because of the design of the direct injection system.
The fuel being injected directly in the combustion chamber isn’t going by the intake valves, like conventional combustion engines, causing the oil vapors to turn into carbon on contact with the hot intake valves.
In comparison on a conventional combustion engine the injectors are in the intake manifold, before the intake valves, so when fuel is injected it cleans the intake valves at every injection cycle.
BMW developed a valve cleaning process using walnut shells that we now offer for BMW Audi and Volkswagen engines.
The service requires the removal of the intake manifold to gain access to the valves, special adapters then fit over the intake ports to blast the valves with walnut media. On the VW and Audi engines we also remove the injectors to decarbonize them manually and also reseal them to the head.
Common issues related to carbon buildup on the valves are misfires, lack of performance/sluggishness and decreased fuel economy.
This service should be performed every 100,000km to keep your car operating to factory specifications!