1989 Crown Victoria LX, 302 Eng, loaded.

The idle rpm dropped to a point whereas the engine would not stay running...... Vacuum leak/break? If so, the most likely area?

As it stands... necessary to keep gas pedal depressed with right foot, using left foot on brake pedal to control the speed of the vehicle... spooky!

 

Sounds like you are on the money with a vac leak.

Have you tried to spray a little brakekleen or carb & choke cleaner around the vacuum lines and intake manifold.
Don't forget to check the vacuum reservoir ..