http://www.underhoodservice.com/direct-injection-engines-develop-carbon-deposits/
"...If you look up direct injection carbon deposit problems on the Internet, engines from BMW, Audi and VW always rank the highest. Engines from GM and Ford that have been on the road for at least four years hardly have a carbon deposit complaint. What’s the deal?
Some direct injection engines have bad timing. The modern engine typically has variable valve timing and even cylinder deactivation. The engine management system can control when, how long and, in some cases, how deep the valve goes into the combustion chamber. If an intake valve is dropping into a combustion chamber with combustion byproducts or unburned fuel, the valve might be exposed to the precursors that cause carbon build-up.
Some have blamed the positive crankcase ventilation (PCV) systems for leaving an oily film on the intake valve that is then baked into carbon. Some blame the valve overlap during the intake stroke that eliminates the need for an EGR valve.
The Fix
There are several fixes available to solve carbon build-up problems.
The first is preventive maintenance. Scheduled oil changes can keep the camshaft actuators working in optimal condition to control the exposure of the intake valves. Spark plug replacement can reduce the amount of unburned fuel in the combustion chamber that can stick to a valve. Fuel injector cleaning can help injectors maintain the correct spray geometry.
But the number one method for preventing a carbon build-up problem is updating the engine management software. New software can reduce carbon deposits by reducing the exposure of the valves to conditions that cause carbon build-up by adjusting valve and spark timing.
Don’t assume that you will find a TSB saying that a reflash of the ECM will correct a carbon build-up problem because most of the updates will be contained in normal housekeeping that may never say anything about a problem. You may even have to check the OEM’s website to see if the vehicle has the latest version of the software..."