My car gets a tad jumpy when at idle when it's warming up, and the engine is a little loud. Well, I thought nothing of it and replaced my tank with 89 octane. After I parked the car for 2-3hrs, the engine got cold again here in Minnesota. I warmed up the car and drove home. The butt dyno didn't feel the jitter the 87 octane. I'd have to say the engine runs like it was new again... really smooth. I just don't know if performance can be affected with the change. Does anyone have/worked with this problem?