airfilter box change from " engine type " and accessibility in engine bay. Normally in Islamabad Air filter can be changed after 5000 - 8000 kms. down south from RYK the conditions are more dusty and air filter shall be changed between 3500 to 5000 kms - Random blow cleaning is highly recommended. OEM new or replacement from reputable brand is fine. Fuel average drop is normal when BAD quality air filter is in the box