A number of factors cause excess carbon build-up on the intake manifolds of TDI engines with the ALH engine code. Although cleaning of the intake manifold is not on the factory maintenance schedule, this is a very important service that should be completed when there is significant carbon build-up in the intake manifold.
Allowing the carbon to continue to build up can cause many issues including reduction in fuel economy and performance, limp mode, a stuck anti-shutter valve that will prevent the engine from starting, or even a complete runaway if the air cut off safety function is compromised by the carbon build-up. Don't wait for any of these issues to occur and clean out your TDI's intake before it becomes clogged any further!
