I've some old gas in one of my cars that I don't drive. I start it and let it run occassionally, but the gas has gotten old enough that it will not idle at all. I have to continuously feather the throttle. What can I add to it to make it run enough that I can burn the old gas out of it? Isopropyl alcohal? Octane booster? Something else? I could probably add just add several gallongs of premium gas to it but I don't want to add more gas to it, just to have it go bad again in the future.