My 91 Camry is down and out for now from engine gunk, and I'm wondering if I should have been putting premium grade in it instead of regular.

My sister had an 1986 Chevy Nova/ Toyota Corolla that would break down in traffic if bad gas was put in it, but was otherwise very reliable. I have heard some mechanics say grade is everything, or also that it means nothing.

Do you think there is any difference in the grades?