Since I was doing slarkplugs, I decided to carbon clean my valves too. Now that's I've done it, I think I will move to 80k miles intervals or ever two sparkplug changes.

I bought a media blasting hopper from harbor freight along with their blow gun kit. Then I bought a spacer from Lowes to fit the blow gun wands I to the hopper airgun. I already have a 26 gallon air compressor. I also bought a port cleaner adapter on ebay and 25lbs or 18/40 walnut shell (you really only need 10lbs for this job). Those items along with a new intake manifold gasket cost around $140.

The mk8 intake manifold has a few differences to the mk7 manifold so the YouTube videos you will find will not show you everything. There are a lot of connectors and vacuum tubes to disconnect so be extremely careful when you get ready to remove the manifold. Removing the oil filter helps a ton too. Once the manifold was off I removed the little air redirect slots and blasted them separately. Then I worked on one port at a time, moved the piston to TDC with the sparkplugs removed and then soaked the valves in valve cleaner for about 10 minutes. Sucked out the clear and wiped them down with a rag. I put the port adapter on along with the shop vac and started blasting with the valves. I would stop every once-in-a-while and check my progress. Occasionally I used a pick to help break bit of carbon off. 

That is it. I would repeat that for the other valves and then reinstall everything with the new gasket. I would recommend putting a rag over the other port opening, I take tube, and oil filter to keep the walnut shell out.

Pic is of cylinder 4 which was the worst of the valves. Then an after pic of I forgot which piston.

Carbon cleaned my valves. 46k miles.