How often should you change your air filter and could a dirty one cause a decrease in gas mileage.

Thanks.

 

Every 6 miles.

If it looks dirty/clogged change it. Eyeball it. Just remember a little trapped dust isn't going to kill you, but if it looks bad then it probably is bad. You could probably just put your hand against it to feel for suction. If you have a K&N or K&N style filter, you can clean it rather than tossing it.

 

in the car maintenance manual, it says every 30,000 miles.