1998 Ford Mustang gas

It depends on how far you drive each day. Using fuel injector cleaner will be alright and will help clean the injectors to work better. With 100,000 miles you can use some throttle body cleaner. Follow the instructions on the bottle, throttle body cleaner will clean out some of the built up carbon in the throttle body. It is sprayed in where the air filter is usually there is some build up in some cars.