After spending a week experimenting with different octane grades I've gone back now to 93. However, I'm still getting a strange idle where it will slowly rev from 800-900rpm up to about 1500rpm hang, and then fall with a shudder. I'm on my first full tank of "pure" 93 and still having this issue. As I was driving home tonight, my car threw a CEL, I don't notice anything other than the weird idle, no loss of power, strange noises etc...

Any ideas? I'm going to reset the battery in the morning, if that doesn't work I guess its off to the dealer, who knows, maybe there is a "N" flash now

 

Don't think its the fuel....maybe a problem with the drive by wire throttle....

 

Yah if the light comes back on take it in.. I bet its somthing to do with the (cat)...

 

after hitting the dealer, turns out it is a weird problem with something in the throttle body, they have to order a new one as the part is not accessable due to EPA regs, so long story short, I guess it isn't the gas, which is good. Once I get it back I'll report on mileage and idle.