When your car gets a lean knock, it reports it to the ECM. Quit being cheap and buy the right gas. I have a solution though. Fill it up with 93. At 1/2 tank fill it with 89. That will make it 91. Next 1/2 fill with 93 then after that 89. That's what I do.
It's not even a matter of being cheap the salesman that I bought it from specifically told me to use premium. now the problem gets even weirder at 3/4 of a tank Check engine light comes on at 1/3 it goes off thats using premium