Originally Posted by Slider
I've got a co-worker that had that issue with his VW. He got rid of it due to those problems and bought a 3.6R earlier this year.
That's part of the reason I'm selling my 2010 GTI. Right around 40k is when the buildup gets bad enough that it causes reduced performance/fuel mileage and an occasional CEL at idle. I didn't have it cleaned until 70k but it costs an arm and a leg to do so. Performance was completely restored after the cleaning though. Other manufacturers have the problem to a lesser degree. It's some combination of crankcase gases/no fuel/cleaners in the intake ports and aggressive valve overlap.
Ford apparently doesn't have the problem in their ecoboosts from what I've read (they say they've solved it via engine tuning). Toyobaru's port/direct injection should alleviate the problem in the BRZ's. I believe Subaru's own design doesn't involve port injection but I've read that they aren't anticipating buildup problems in their DI engines either because of good design/tuning.