Where am I... what year is this... why didn't the guy at the auto store put a scanner on it and read the code?? Problem indicated... solution imminent. I guess he really wanted to sell that Seafoam

Octane ratings are calculated differently in different parts of the world, so 92 or 99 in Europe may not coincide with the same numbers here, yes?

Octane boosters do work... they are not snakeoil. Torco or Lucas are the most popular brands.

Cars that call for premium gas, should get premium gas. Sure the knock sensors will pull 5 to 20 degrees of timing and keep things putting along... but that's because... your engine is DETONATING from the lower octane.