Carbon build-up can be a somewhat common problem on modern vehicles (particularly those with direct injection). Carbon and engine oil can build up on the back of the intake valves in the cylinder head and inside the intake manifold because the traditional fuel injector that would sit in the intake manifold isn't spraying/washing the back side of the valves in this design. How do you get the carbon buildup out of your engine parts you ask? Driven SD has the tools to do a walnut blast (think of sand blasting but with a much softer media than sand....Crushed walnuts). Pressurized walnut dust is used to clean the engine parts while using specially designed tools to fit your BMW engine and vacuum the ports as you go. This is a specialized service that a lot of shops probably wouldn't offer for your BMW, luckily you already found Driven SD and this is the place to do the job at a much better price than the BMW dealership.