How do I maintain the K&N air filter?

Purchase a K&N air filter cleaning kit from your favorite vendor. It is comprised of cleaning solution and spray-on oil. Follow the directions on the box - basically, soak the filter with water/solution mix, rinse and allow to dry naturally. Then apply the spray-on oil lightly and evenly until cotton gauze is red in color on both sides. Reinstall.

Never force dry the filter using compressed air, heat, etc. Also, never brush the filter in an attempt to clean it. This will damage the cotton gauze. You shouldn't need to clean the filter until you can no longer see light shining through the cotton gauze when held up against the sun or a bright light.