If your vehicle has a direct fuel injection motor, it is prone to carbon build up around the valves in the intake ports. This is a common issue for engines equipped with direct injection and will require strict maintenance intervals to prevent. If your vehicle has direct injection and exhibits some of the following symptoms, there is a good chance may have carbon build up in your lower intake:
If caught early on, a small amount of carbon deposits can be removed through a special direct injection induction service. However if the deposits have become too thick, the upper intake will need to be removed and the lower intake will need to be walnut blasted to break up and remove the contamination. This procedure is very labor intensive, therefore very costly, so it is best to keep up with the preventative maintenance geared towards these carbon deposits. Below are a couple pictures of a supercharged Audi Q7 that was in for walnut blasting.