EEMan

On the contrary, it is expensive. The intake manifold does not just pop off. There is a lot of interference to be removed--fuel lines, etc. it is very labor intensive so probably several hundred dollars. With respct to detergent gasoline it does not help the back side of the valves because it does not come in contact with them. Also it seems that much of the carbon comes from crankcase ventilation.

snagitseven

True, but the cost is considerably less than the old method of removing the manifolds and soaking them in a cleaning solution for a couple of days. That process is significantly more labor intensive and costly than the $400-$500 of a walnut pressure cleaning.

breadbooze

The buildup comes from the lubrication of the valve stems that causes particles in the intake air stream or blowback from the combustion process to stick and burn in minute quantities. Detergent gasolines can't help much since the fuel is sprayed directly into the combustion chamber in DI as opposed to older port injection systems where the air/fuel mix happens just before the intake valves and thus exposing the valves to the detergents. Particulates in the intake air on DI engines come from the crank case vent and EGR, so using a catch can for the CCV and a EGR delete could minimize buildup, though the car would fail emissions.

Audi service can do the work, I believe it's 3-4 hours T&M.

EEMan

This is sounding a little better. I watched a video on the soaking method which seems quite laborious. I recall from Navy days that crushed walnut shells were fed into a running turboprop engine on P3s. I also read a piece from a UK source suggesting again that operating at 3000 rpm occasionally will help and noting that slower turning V8 DI engines experience carbon more often. Thanks for all the helpful posts.

snagitseven

Just to clarify, the walnut shell process on a DI engine is done without the motor running. In fact, great pains must be taken to avoid any of the shells from entering the open ports before cleaning and after the shells are vacuumed out. I can't imagine what would happen to the valves if there were shells remaining when the engine was started.

EEMan

Of course. I was commenting hust on the cleaning effects of the shells, not the process. Thanks for clarifying.