1989 Cadillac Deville Car Will Start But not Idle.

I have a 89 Deville 4.5 with 67,000. I bought the car form a young girl who said it ran rough before parking it. I got it started by having someone turn the key and I moved the throttle. That is the only way I can get it to run. Once I let go of the throttle it dies. When you turn the key it wants to start but does not. There is an exhaust leak sound while it is trying to start. Also if you leave it sitting for a couple of says and then try to start it, it will run for 5 seconds and then die. New fuel filter, plugs, dist cap, coil, wires & battery. Thanks for any help.