Fair warning to anyone considering buying a car with direct fuel injection (DFI) like an RS4. My car is in the shop this week getting a "de-carb." That is, they are taking-off the intake manifold and manually (yes, by-hand) cleaning all the carbon build-up off the valves. Luckily, I've still got six months of warranty left. Seems that with DFI, the gasoline, including any detergents or pour-in cleaners, never touches the valves/intake manifold. So when PCV (positive crankcase ventilation) vents into the intake manifold via the oil separators, which are ineffective at low RPM, the vaporized oil just condenses on the valves with nothing to clean it off. Poor design--don't know why PCV doesn't just vent back into the air system upstream of the air filter like my good old '71 Olds! So if you plan to by a car with a big engine and DFI, better have a plan for running it out (fast & high RPMs) regularly. 20 Kmi or so commuting with cruise control at 65 on I-5 just didn't cut it.

 

I just became a member here, and am not sure if this info is new to these forums but it certainly isn't anywhere else. This is a problem with any direct injection engine that doesn't also run an additional port injector (ie. Lexus IS-F). The 4.2 FSI in the RS4 is no different.
Also, it hasn't been found that constant high RPM use is a fix. If you're shop told you that you could eliminate it by driving 10/10ths all the time, don't believe it.
Constant steady mild RPM may slightly increase the rate of build up, but either way the 4.2 FSI could use a carbon cleaning every 20-30K miles no matter how you drive it. Nature of the beast I guess.
There's MANY DIY's out there for the procedure and it's fairly easy. I can do it in about 5 hours by hand and some BG ISC to loosen the buildup.

 

Waaay back in 2008 when I had my RS4 is for its first manual valve cleaning, that's what the tech said..."just drive it hard". Why would he say that? Because he's applying a 1980's fix to a 1980's problem. Apparently, me driving the crap out of the car wasn't hard enough. Since early 2008, there's literally thousands of forum posts relating to DFI carbon build-up and supposed fixes. None of it works. Why? With no solvent action of the fuel spraying directly on the back of the valves like a non-DFI engine, the carbon build-up is impossible to avoid. I cleaned my valves myself four times (about every 10k miles). I got fed up with it and sold the car. Some RS4 owners are so enamored with the appearance of the car, they continue to put up with the insanity. Good for them I guess...they must not have anything better to do than regularly pull the manifold off a $65k car. If you truly want to avoid carbon build-up on an RS4 1) don't drive it 2) sell it.