How often should I change my engine air filter?

I have a 2003 Toyota Corolla....how often shoudl the engine air filter be replaced?
How often should I change my engine air filter?
about every 2 or 3 oil changes depending on how many dirt roads you travel on. If it is all pavement you are good with the 2 or 3. If you have a lot of dust being sucked in every 2 oil changes.
How often should I change my engine air filter?
As a rule every 15000 miles unless you travel dusty roads or some other dirty condition
Your owner's manual may give you the best information for your car. Your car dealer is also a good source. Generally, you can go about 20,000 miles under normal conditions. If you buy a K%26amp;N air filter, you can wash it whenever you like to clean it and it lasts the life of the car. http://www.kandn.com
I lived near the desert and I changed mine once a month to be sure...8 bucks a month was easy to keep your car engine cleaner...not sure if it was a benefit or not but I did it anyway.
I have mine changed every two oil changes. I don't live on a dusty road, but it's fairly busy and there's always dust flying from the traffic.