1996 Ford Explorer up down idling engine somtimes wants to

You have not mentioned if the check engine light is on....if so, DEFINITELY have the trouble codes read before proceeding further. If engine is idling up and down repeatedly, I would suspect the idle air control motor is bad. When the ECM receives signal from the throttle position sensor that the engine is at idle, it uses the idle air control to regulate air flow into the throttle body, thereby regulating idle speed. Sometimes this can be fixed by simply removing that IAC and cleaning it out with carburetor or throttle body cleaner as they can get quite dirty.......you will find the IAC on the throttle body with two small bolts holding it on and a two wire plug.....