That tune up really did the trick, didn’t it? Gas mileage is up and the engine even seems to have a little more power now that it’s running smoothly. You may feel tempted to give it a little extra gas now and then. But, if you have too much fun with that extra power, it may not save you any money at all. It might even wind up costing you money.How? Well, first of all, those jack-rabbit starts