There are some little things you can do with your vehicle that will save you some gas and make your vehicle run better. Doing engine performance maintenance will keep your vehicle running properly and improve your mileage by 4%. Fixing a serious issue can improve your mileage by 40%. Some smaller things, but just as significant are: proper tire inflation (3.3% improvement), proper type of motor oil (1-2% improvement), new air filter and replacing a damaged, loose or missing gas cap.
(car care council )