Hmmm...I was worried about this. So, how can they diagnose carbon buildup? Do they have to use a borescope down the intake? This concerns me because I think my 335 feels slighly less zoomy than some that I test drove.
I wonder if spraying some fuel injector cleaner or even windshield washer fluid down the intake now and then would help?
Hey...I just remembered...has anyone heard of GM top-end cleaner? A lot of people swear by it. I wasn't sure about using it on a turbo motor, but I googled and found this on a GMC Typhoon forum...
GM's "Top End Cleaner" - knock reducer in a can.
Basic principle is that the PCV system spits oil back into the intake, carbon gets built up on the heads/valves, and result in detonation causing, raised hot spots.
This stuff is pretty simple, suck it in while the engine is running, let it sit in the combustion chamber for some time, then burn it all off.
There are 2 versions of the Cleaner, spray, and liquid in a can. I've used the spray can, and many others have used the liquid version.
The can leads you to believe its for carb engines leaving you somewhat clueless on where to spray it. My solution was to remove the upper Ic, and spray the cleaner directly into the throttle body. You can just leave the outlet of your turbo open for this, just be careful not to drop anything in there. With the engine running, and your hand on the throttle lever, start spraying into the intake. The cleaner will cause harsh idle, and you may wish to give it a little throttle by rotating the throttle lever slightly as it tries to die (also helps suck in more cleaner). Continue feeding the truck the entire can. When your almost out, go ahead and try to stall it out, if you don't succeed then just shut off the truck. You want it to sit and allow chemical reactions to clean up your cylinders for a good amount of time, the can says 10-20 minutes, you can wait longer. You'll probably notice it smoked alot during the process, and is probably still smoking while you wait for the scrubbing bubbles to do their work. Wait till you start it up again. The resulting plume of smoke should make for a good impression on the ricers next door. Changing the oil is a definite next step. Im not sure about the cleaners effect on the spark plugs, but you may consider doing a fresh ignition at this point. After the smoke clears, you should feel strong and ready to burn off some boost.