This is the n80 purge valve, the description explains it better than I could: Audi B7 A4 Quattro 2.0T > Search > Purge > ES#281033 Purge Valve - 06E906517A
It's part of the fuel system. The diverter valve is on the turbo and helps in regulating boost.

I've used the seafoam spray method to remove carbon and that worked well, and periodically throw in some techron to keep injectors clean.
Techron/12 oz. fuel system cleaner (266362) | | AutoZone.com

Yes snub is easy, just a few bolts.

Cheers.

 

All of the little things mentioned are very easy to do. Don't consider it a "waste of money" consider it an "investment in longevity".

These motors idle rough. I hate it too, and they seem to run even more rough at idle when you tune them from my experience.