Idle Issue

You can try;
- Richen up the mixture by turning the idle mixture screw out half a turn orso.
- Increase idle speed of the engine. Any idea how much rpm it is running when it does?
- Hook up a vacuum gauge and report back the number you're seeing on the gauge. After 20 years, one or more piston rings could be stuck to the piston and create a lousy engine vacuum. Also, bad timing adjustment can create low vacuum too, as a few other things can.