A dirty air filter will lead to reduced performance and increased fuel consumption, necessitating renewal at specified intervals, especially in dusty conditions where more frequent changes are required. For carburettor models and the PM engine with Mono-Jetronic, start by releasing the spring clips at the edge of the air filter cover, unscrewing the single screw, and withdrawing the cover from the air filter body. Next, lift out the air filter, wipe clean the inside of the air filter body and cover, then place the new filter in the body, refit the cover, tighten the screw, and snap the spring clips into position. For fuel injection models, except the PM engine, release the rubber strap on the right-hand front corner of the engine compartment, pull out the intake cover, and disconnect the intake hose. Remove the screw to withdraw the side cover, then release the spring clips securing the air filter cover and lift it from the airflow meter to access the air filter. Remove the filter from the main body, wipe clean the inside of the air filter body and cover, locate the new filter in the body, refit the cover, snap the spring clips into position, and finally, reattach the side cover, intake hose, and intake cover, securing everything with the rubber strap.