Did you know that carbon build up occurs behind the valves hence fuel never reaches it because it is a direct injection engine and your additives have absolute zero effect? This model has a major recall due to this with some tragic consequences like piston set replacement or even entire engine... It's a flaw in design and sooner or later you will notice rough idle at stop light or cylinder misfire codes at startup. I urge you to do a valve clean up every year. That is the reason why I didn't buy this car.
Also did you know why IS350 is not affected by carbon build up issue? Because it has direct AND port injection which means fuel flushes valves.
