1974 Dart

To idle
your engine needs
1) fresh fuel
2) a sealed intake tract.
3) a good working low-speed circuit,including the bowl vent
4) a properly adjusted speed screw.
5) valves that close. and open. and at the right time
6) reasonable compression, in every hole
7) reasonably close ignition timing, and a good working ignition system
8) a clear exhaust system.

To stay running ,above idle, your engine needs all of the above as well. But, it is less sensitive to a problem in any one area.

At idle; 1 thru 5 are very important, and 6 to 8 only a little less so.

From your description it would be easy to point the finger at 4,1,3,2; in order of ease to check/verify.