94 LINCOLN Cont. Shuts Off After Start Up

[hhlincoln]

Hello,
I just bought a 1994 Lincoln continental 3.8L. The car turns over then shuts right back off. If I keep my foot on the gas it will stay on. Sometimes after pressing on the gas pedal for a while then releasing it, it will idle erratically for a few seconds to a few minutes then shuts off. The car drives fine, but when I press the brakes it sometimes shuts off. I have just changed the oil, plugs, air filter, fuel filter and pcv valve.
What could be the problem?
Thanks in advance for your help!