sounds like a little ground water got into that tank....lol....we have a very smart car, and it will compensate, and remember...feed a dog cheap food and he may not bite you, but he may not be your best friend either, feed him right, and he'll love you to death...our cars run best on the octane recommended, simple as that. Why make it retard all the time and burn that memory into the computer? I still think it harms the engine with more heat and stress over time, like when you get into the 80-100K range...just me...