How often should the engine air filter be changed? 

Your car's engine air filter should be changed regularly to get the most out of the engine and prevent premature wear.
If the environment where the car moves is not very polluted, then you should change the engine air filter every year at most or the equivalent of 15,000 kilometers.
If there is greater contamination, for example: dusty places, with a high level of soot, sea sand and salinity, then you should change the air filter at a maximum of 10,000 kilometers, about 8 months maximum.
Changing the engine air filter is quick and easy - it takes about 5 minutes and the cost of the air filter is about $6.00 ($6).