Answer: Dirt and debris build up over time and clog the pores on your engine’s air filter. Generally, you should have your air filter replaced every other time you have your oil changed (about every 6,000 miles). At the very least, you should have your air filter changed once a year. However, depending on where you live and the conditions of roads on which you drive (dirt or dusty roads), you should check your air filter every time you change your oil. This regular maintenance can lead to better engine performance and gas mileage.