Car started but died when i let off the gas now it wont start period?? please help!?

okay, im a mechanic and im boggled. i have a 1994 ford probe gt 2.5 v6 DOHC. i recently bought it as a project. the timing belt had snapped going around 45. it had bent valves and all that. i replaced the heads. timed it. bought a new distributor and all that. it was running real good and smooth but when i let off the gas pedal it would die. so i tried timing the distributor and when i tried it completely died. the motor still turns over and has kind of a popping sound underneath the car so it sounds as if it is getting fuel and fire. previously the car sat with a 3/4 full tank of gas for 2 years! still the same gas in it. so my thinking is the gas is is no longer potent enough to combust. any opinion would be very nice and helpful. before anyone asks. yes i have checked the timing over and over. it lines up everytime. no wires or sensors were knocked loose. i have checked them over and over. everything is grounded. all fuses are good. fuel pump is brand new and it it is still pumpnig gas like a beast. i have checked it. it is getting fire. all spark plugs and wires are in the correct places and fully connected. all fuel lines and filters are unclogged and connected properly. there is plenty of oil. so any opinions or advice would be great. thanks everybody!