Engine Surge/Races on 1998 F-150

My engine started to surge when the A/C was turned on and no its doing it when the heater or defroster are turned on. It does it when the egine is idling and when it is in motion. Actually causes the truck to lurch foward when stopped at a light. Any advice.

does it do it when set on just the vent or just the floor, because when in the dual mode ( vent and floor) and a/c will be engaged.