When I first installed the CAI and 93 tune I'd use Sunoco's 93 octane with 10% ethanol. Didn't think much about it. Car ran great. Then I read on this forum (this was many months ago) the same comments as above...don't use ethanol if you can avoid it. So I switched to Exon 93. I got a tell you, its better. Its a subtle difference but the car does get better MPG and seems a little smoother, more responsive. Fortunately its easy to find in PA.