A well-tuned car can run 4% more efficiently than one that is out or tune or has failed its emissions test.
According to the Car Care Council, regular tune-ups, maintenance, and having clean air filters will help your car pollute less and burn less gas. Getting a tune-up can improve gas mileage by an average of 4 percent. Simply changing the car’s air filter can improve efficiency by 10 percent. Fixing a serious maintenance problem, such as a faulty oxygen sensor, can improve gas mileage by as much as 40 percent.