An air filter is an important part of a car's intake system, because it is through the air filter that the engine "breathes." An engine needs an exact mixture of fuel and air in order to run, and all of the air enters the system first through the air filter. The air filter's purpose is to filter out dirt and other foreign particles in the air, preventing them from entering the system and possibly damaging the engine.

An air filter for your car will generally be pretty cheap, due to the filter's simple construction. An air filter is generally a paper-like or fibrous material, folded accordion-style and arranged on a plastic or metal frame to fit your car's air filter holder. An air filter can also be made out of a cotton- or fabric-like material, which is then oiled in order to increase airflow through the filter. The air filter holder is usually a plastic or metal box in which the air filter sits. Generally, the air filter holder is connected to the intake manifold by a large plastic tube through which the air flows.

A clean air filter is important for your car's performance. This means that your air filter should be changed regularly, or your gas mileage will suffer. A dirty air filter can also cause other systems to run ineffectively, such as your emissions control system, which regulates the car's air-fuel mixture. A dirty air filter can also cause your spark plugs, which ignite the fuel in the combustion chambers, to foul, as there will be too much fuel without enough air; if your spark plugs foul, you may have problems keeping your car running.

Your car's air filter should be changed at least once a year. However, an air filter may need to be changed more frequently if you live in an area with dirt roads or heavy pollution, as these factors can cause an air filter to become dirty more quickly. You can have a mechanic inspect your air filter, and change it if necessary, during an oil change or your yearly tune-up.

If you plan to change your air filter yourself, look for a large plastic tube leading away from the top of the engine. The tube should connect to a large box that may be round or square, plastic or metal. The air filter box will have a top that comes off to access the air filter. If the filter material is blackened, the dirt is restricting the passage of air and the filter should be replaced.

Replacing your air filter is one of those simple jobs that you should do regularly to maintain your car's performance and extend its life. Nonetheless, the air filter is often neglected, either out of ignorance or forgetfulness. You may find that keeping a record of any maintenance done to your car, along with the date and mileage, helps you to remember when your air filter is due to for inspection.