I'd make a strong bet for a vacuum leak. Check the hose connections from the carb area to the vacuum modulator. The modulator is on the bottom right side of the C4 trans. The hose often works loose from age. I suggest replacing that hose.
Check the PCV hose from carb to valve cover and check the PCV itself. It should rattle. Sometimes they get gummed up inside and don't work right even though you think its okay. It wouldn't hurt to replace it (cheap $2-3). Especially check the gromment in the valve cover that the PCV goes into. Pep Boys has them but I don't know the part number. Just take the old one with you and match it up at the store.
Cap, points, rotor are good? Spark plugs and wires good?
Check the PCV hose from carb to valve cover and check the PCV itself. It should rattle. Sometimes they get gummed up inside and don't work right even though you think its okay. It wouldn't hurt to replace it (cheap $2-3). Especially check the gromment in the valve cover that the PCV goes into. Pep Boys has them but I don't know the part number. Just take the old one with you and match it up at the store.
Cap, points, rotor are good? Spark plugs and wires good?