'93 grand am stalling...please help!!!

i bought a grand am off my cuz and it had a clogged c.converter.i was broke at the time so i cut it off and staight piped it.it ran better but still wasn't right.i replaced the plugs,coils,coil housing,O2 sensor,map sensor,starter and ecm.now it runs like a champ except when i hit the gas too hard in park or sometimes when i'm driveing it just cuts out.very rarely will it start right back up.it sounds like it wants to turn over but won't.i rigged it to give it some back pressure...still no luck.there is one plug(i believe it comes out of the same harness as the crank sensor) that isn't plugged in but i can't find a home for it.i am loseing my patiance very quickly with this car.the body and interier are too nice to junk it.plus like i said...the engine sounds strong and runs great until it stalls.any suggestions?

the only problem ended up being the spark plugs i bought.NEVER buy bosch +4 plugs.i put the cheap a/c delco plugs in and it runs much better with no stalling.