Well actually you are supposed to let it idle, at least that is what the prez of Wildcat fuels says. I read an article that says every engine goes through a process called " hysteresis ". It also said that 99% of the time your engine will be fine if you dont let it idle, but for that 1% it will last a little longer. But anyways, i used to do what i8tweety does when i switched fuel, which is great, never had any problems, but now i just use Trinity fuel.