Hey, so I had someone using the car and they put a whole tank of Regular 87 in the tank. I've only used 93 and occasionally a little 91, but never more than half. Got a code after driving 80 miles on 87. Put an entire tank of 93 on top of it with 90 miles left. Drove it a couple days and the light went out. Put a full tank of 93 in, code went away. Drove 70 more miles, code returns.