Just filled up the tank with 91 octane premium fuel

[A-Dingo-Ate-My-Baby]

Originally Posted by The Spectacle

I'm digging this up from the dead rather than creating my own thread because I'm sure it would just spiral down the same road.

I've just filled up my tank with 89 after 3 years of nothing but the 87 and there is DEFINITELY a difference in throttle response and midrange power. I'm still a bit shocked myself but its there.

I read through a few of these responses and its clear that not many of you know how knock sensors and timing retard/advance work. That's all well and good but I just want to state for the record that Yaris behaves slightly different if you put higher octane in it.

this may be because 3 years of carbon buildup on the pistons incrementally increases compression, therefore if you are having the knock sensor retard timing...higher octane will reduce that somewhat... which translates into smoother power. 3 years of buildup is just a thin layer but will increase compression [and small carbon chunks also create points for detonation to occur]. minor overall effect but that could be the reason for smoothness. still won't go any further down the road with higher octane, but I bet it can smooth the power delivery. if you wind on the yaris all the time there will be less carbon, or if you seafoam it, or use bg44k, that sometimes makes carbon chunks flake off and they get burned up at the cat...but by far the best thing is pull the head and use direct solvent or steam on the pistons, that removes carbon. [of course you are looking at a lot of work for an incredibly minor issue.]