Direct injection cars, and Audis/VWs in particular, seem to have issues with carbon build-up on the intake valves. As fuel is directly injected into the cylinder, the fuel does not get a chance to clean the valve & port. Below is a good image of the difference between the two:
This means that no matter how good the fuel that you use is, how many detergents it has, that won’t actually matter for the valves (will still clean fuel injectors). As such, carbon builds up over time on the valves. The carbon comes from the PCV system, as the system recirculates blow-by back into the intake, which is part of the air mixture. These build ups can lead to a variety of issues, and can lead to engine failure.
With my Golf having 104,000 miles, and not being certain of its history, I decided it would be prudent to have this service done before my first track day. I took the car to Kinetic Motors to have this service done, which includes uninstalling the intake, cleaning, and walnut blasting the valves. A new OEM gasket was reused to reinstall the intake. Below are the results, before & after:
The shop actually commented that the intake valves didn’t look too bad, and certainly this wasn’t the worst I’ve ever seen – regardless, for the peace of mind, I’m glad I’ve gotten this completed now before the first track day. As far as interval, I don’t anticipate that I will have to do this again during my ownership of the car, but we will see.
The other thing the shop was able to do for me was to finally get the damn clutch bypass relay on. The clip was broken and I was unable to get it off the car – fortunately, the shop had the know-how, tools, and patience to get this done – for only $52.50 labor that. Well worth it, and the car now starts without the clutch pushed in.
QL Motorsport & Car Journal 