BMW introduced the N54 engine in 2007 with the 335i and later in the 535i/135i as well. This new engine introduced a direct injection fuel system. Direct injection engines spray fuel directly into the combustion chamber. These engines are prone to heavy carbon build up on the valves and intake tract due to fuel now entering AFTER the valves. Standard engines have fuel entering before the chamber which help clean deposits and minimize carbon buildup on valves. Our cleaning process uses fine walnut shell granules and pressurized air to clean the valves and intake tract. We take extra time to ensure all the valves are fully cleaned off. Enhanced throttle response, smoother idle, and improved fuel economy can be noticeable after this process. We recommend this every 30,000 - 50,000 miles are all direct injection engines.