Changing an Air Filter. Before you start heaving luggage out of your car's side windows or imposing passenger weight restrictions to improve your vehicle's mileage, check the air filter. A dirty or clogged air filter can alter your vehicle's gas mileage by up to 10%.ext, remove the filter and inspect it for dirt by bending back the paper ridges. If deemed filthy, go purchase a new one. Insert the new filter and make sure the casing is tightly secured. Not only is this fast, but cost efficient. Most quick lube shops charge up $20 to change an air filter.