You have bad plug wires. With the engine cold, remove the cover from the distributor cap. Gently break the plug wires loose, remove them and reinstall them one at a time. Now start the engine and remove the wires one at a time with an insulated pliers or better a solid plastic pliers purpose made. The engine will miss as you remove each wire untill you get to the bad one where there will be no change in the miss. Sometimes the car has to be warmed up for this to work. My last one had to be warm and idling in drive with the park brake set and a second person firmly holding the brake to induce the miss. DANGER! DO NOT RUN OVER YOURSELF DOING THIS!
Good luck.
Harold