I just recently started using Lucas Racing Oils fuel injector cleaner. They reccomend a bottle (about $4 at the auto parts store) in a tank of gas every 3-4 thousand miles. So basically when you change your oil. It also contains a top end lube for the valve train. It might all be in my head but the engine sounds smoother/quieter after and I also noticed a 10-15 mile per tank increase!