2003 Kia Optima car hesitation

last week i attempted to pass another car. as i accelerated the car reacted normally. but after i passed the slower car, my engine stalled. i put the engine into neutral and was able to re-start the car, but i could only keep the engine running if i feathered the throttle. after i stopped the car the engine died. i was able to get it re-started but was only able to keep forward momentum if i kept the accelerator pushed completely to the floor. this would accelerate the vehicle but if i let off the accelerator the engine would die.