1989 GT 5.0 Start up and Idle concerns

hey everyone, i just picked up a 1989 Mustang GT 5.0 automatic a couple weeks ago (all stock besides spectre air filter) and im having an issue with startup. whenever i turn the key over the engine will start but if i dont give it any gas, it will just die on me. it also likes to die on me when i am idling at a stoplight and try to take off. i also feel like my engine isnt producing the ammount of power that it should be when i mash the pedel to the floor. i think it may have something to do with the air to fuel ratio but i am not sure of this. does anyone know what may be the problem?