While installing my dp and fmic. I was chatting with my friend about checking the carbon build up. (He is as VW mechanic). He checks by viewing through the plug holes ( with a scope) and turning the crank by hand. The mini crank seems hard to access plus the intake is on the firewall side.
how do you guys check carbon build up?

 

If the scope has a light.. its doable as mentioned..and much easier to peek at vs, taking the mani off. Ive not done more than that myself so far.

*If your plugs foul up in less than 10k and have a plastering of caked ***** on them, then its a fair guess without even looking down the hole, to assume you need a decoke. Oil consumption is also an indicator. Im changing plugs and oil like its free right now trying to avoid doing the decoke service..though I dont think its going to be wise to keep doing so for long. 78k on my N14 here.