1996 Chevy Truck wont start

Just got it, it ran fine, then fuel got low, it wouldnt start, called seller, he told me to press gas pedal to the floor.I smelled gas like it was flooding but it cranked, got home, let it sit, 4 hours later, it started fine. Went and gassed up, it did'nt want to start again, repeated the pedal to the floor, it had trouble staying at idle, made it home, seller came to house to check it out, took the hose off the throttle body it ran good put it back on it cranked one time then went back to not wanting to turn over. Please help. Thanks