For manual transmissions, you should change the fluid about every 50,000-90,000 kms, however, under intense use, some manufacturers suggest changing it as often.
Ford Motor Company recommends replacing your engine air filter every 15,000-30,000 miles, depending on your vehicle model. Refer to the Maintenance section.
Basic, 1-inch filters, typically need changed every 30 days to 3 months. For thicker, pleated 4-filters, the standard is to typically replace them every 90 days.
If none of the previous issues are forcing you to replace your spark plugs, you can typically change them every 30,000 to 90,000 miles depending on the make and.