Ninety five thousand miles, and I finally mustered up the courage to do a proper "carbon cleaning" job on the GTI. The GTI is a "direct injection" engine, meaning, the fuel injectors are not able to "wash down" the intake valves. Instead, oil from the PCV system builds up over time on the valves and intake port. These photos are from one of the two days it took me to do this job. The job was ultimately, wildly successful. The car was SO much quicker, post-cleaning. And, VCDS no longer displays multiple misfires on startup (and even on running.)