According to factory specifications, air filter has to be changed in every 40.000 km (24.000 mi). If you drive on dusty roads regularly, it is adviced to check the filter in every 2.500 km (1.500 mi) (maybe cleaning), but in this case, you don’t have to replace it sooner than 40.000 km (24.000 mi) – according to specifications.
In my opinion, that is too much. I don’t drive on dirt roads, but air filter isn’t an expensive part, so I replace it at the time of periodic maintenance in every 15.000 km (9.000 miles). It works for me in that way. The cleaner the filter, the better the air supply to the engine, the better the performance and fuel consumption. Not worth the wait for replacement.
Air filter changing is a very simple process.
1. Air cleaner upper case removal
Air cleaner upper case is held by a case nut on the top, four clamps (or three) on the side and it is connected into the air cleaner hose. Remove nut and clamps and take off upper case from air cleaner hose.
Some people remove the whole air cleaner hose. There are some type of cars which don’t have air hose at all and the air goes into the engine right from the engine compartment. As far as I know, air from the engine compartment is better for cold engine, because the engine gets warm faster; air from outside across the air hose is better for warm engine as it contains more oxygen. Anyway, I leave the original construction.
2. Air filter replacement
Remove the filter!
The air cleaner lower case below the air filter is usually a bit blobby. It is because of the sludge and vapoury pollution from PCV hose. This hose always should be as clean as possible. This pollution is less, if you have an oil catch can (not installed originally).
You can insert new air filter only in the right position.