Your air filter defends your engine from ingesting all the dust, all the dirt and other small metal particles in the air. Air filter absorbs all harmful particles and clogs up just like the bag of a vacuum cleaner clogs up. In case if it clogs up, then the engine gets a harder time to suck the air through it hence causes poor engine efficiency. In order to compensate for the decreased airflow, the engine management system will increase the fusion, as a result, it will use more petrol to keep the engine running. So it is highly recommended to change your car air filter after 3000 to 5000 km (subject to the quality of filter and environment) and you will see improved gas mileage.
