When the engine air filter clogs with dirt, dust and bugs, it causes your engine to work harder and your car becomes less fuel efficient. Replacing a clogged air filter could improve your gas mileage by as much as 10 percent and save you 15 cents a gallon. It’s a good idea to have your engine air filter checked at each oil change. The Car Care Council recommends changing your car’s air and oil filters every three months or 3,000 miles or as specified in your owner’s manual.