What is an engine air filter? An engine air filter is a car part that helps to clean the air that enters the engine. The filter is usually made of paper or cloth and helps to remove dirt, dust, and other pollutants from the air. A clean air filter is essential for maintaining a healthy car engine, and it can also help to improve fuel efficiency. Air filters typically need to be replaced every 12,000 to 15,000 miles, but this may vary depending on the car and the driving conditions. Replacing a dirty or clogged air filter can be a simple and inexpensive way to keep your car running smoothly.