An auto air filter's function is to clean the air to an optimal level. An air filter prevents dirt, contaminants and other harmful debris from entering your engine. Normally, it's pretty easy to tell if an air filter needs to be replaced by just looking at it. However, if you're having trouble, it's a good rule to change it every 3 years or 30,000 miles. Having a blocked air filter decreases airflow and doesn't allow enough oxygen to mix with the fuel which makes it too rich. This results in lower gas mileage and puts unnecessary stress on the engine. As it gets worse, you'll notice it in the performance of your car and your check engine light may turn on. At eWorldTrade, we have a collection of air filters that are high in quality and will last you ages. If you'd like to get in touch with the manufacturers of the products and inquire about them, you can easily do so directly. For feedback or help, you can contact our customer support as well.