Please HELP me revive my Stang !!!

[Rodoggx]

Hello,
I just bought a 1990 mustang lx 5.0. It has 86,000 original miles and is totally stock. This is my first mustang and I feel blessed to have found this car for under $1500! It is in near mint condition except for a bit of faded paint! Now that I have stroked my mustang a bit... lemme tell you whats WRONG ...
When I bought it from the original owner, it had been sitting for 4 years and not driven. The thing is, it had a really rough idle. I thought a tune up would set it straight so i put new plug wires, distributer cap, rotor, plugs (gapped at .055), and an oil change The idle smoothed out a bit. When I try to start the car, it will die on me but after that it will start up and run fine. The idle still sounds like it has a miss but sounds better than before.
I just want to know what is causing it to die on me on the initial try. I still have to change the pcv valve, fuel filter, and check timing. But if you guys can think of anything else that might be causing my stang from running smooth, I'm all ears. Do I need to check the TPS voltage or anything else?
I've read many previous posts and you guys have helped many people and seem very knowledgeable. If you guys can lend a helping hand I appreciate it. THANK YOU.