Because the TSI engine is direct-injected, fuel never washes the intake valves and carbon accumulates on them - commenters call the platform notorious for it. Walnut-blast carbon cleaning is the accepted remedy and shows up as a maintenance credential in multiple listings: sellers cited cleanings at 61k, during recent ownership with receipts, and bundled with timing chain service. …
Carbon buildup on the direct-injection valves
Volkswagen GTI (Mk6) · mechanical