I may know a bit more than some...LOL.
My car has been decoked twice.
First at 30 000 miles and again at 65 000 miles,both times when the engine was in bits,allowing easy access to the intake ports and valves.
This is what it looks like before.....
http://i1251.photobucket.com/albums/hh544/s3alex/DSC044241024x768_zps62fe53c2.jpg
http://i1251.photobucket.com/albums/hh544/s3alex/DSC044221024x768_zps686b7b7d.jpg
And after.....
http://i1251.photobucket.com/albums/hh544/s3alex/DSC044251024x768_zpsf4a81065.jpg
On the TFSi,it won't make any difference what type of fuel you use(aside from diesel of course...LOL) or whether or not you use fuel additives,as this is a direct injection engine,and fuel does not enter the inlet tract above the valves.
A catch can will get some of the crap,but not all,because VAG in their efforts to cut emissions,added another breather from the cam cover,exiting into the inlet above the turbo,so whatever happens,you WILL get some oil vapour meeting hot valve stems,and this is the result.
The only surefire way to prevent it is a full PCV delete,which is a pain,as you need a cam breather system,and catch can,and you need to ensure that neither cam nor crankcase pressures rise to the point where oil is blown past seals.
Mine BTW,has had a catch can from 12 000 miles on,and the crap on the valves accumulates despite that,as I've explained.
I'm going to have a new cam cover and breather fitted shortly,and have the extra injector setup running soon as well.....the latter is for more power,but this is a side benefit of an 8 injector setup,but not something I would recommend for anyone not running a big turbo system and needing a LOT of extra fuelling.
For all of us with TFSi engines,the best solution is a regular decoke,and AMDTuning can do this easily and quickly,as was done to mine.
It's a relatively straightforward process,not horribly expensive,as very easy if you have the right equipment.....which they have!
