I would guess that the problem is with the mixer (carb) air fuel adjustment back when those came out sometimes even the factory guys had trouble getting the unit to work.
We had all the tools and program and we had some that took us a while and several parts to get right. One thing I can suggest that won't cost anything is to unplug all of the sensors and controller and put dielectric grease in them any component that the controller
Reads or operates. You could have a bad connection to a component and the grease will help keep moisture at bay