1991 Geo Storm poor milage, black smoke from tail pipe, idl

Engine Performance problem
1991 Geo Storm Two Wheel Drive Automatic 35,891 miles

I am a technician and I am baffeld ! The car came to me with [crank no start] I found a bad ign. Module. This fixed that problem. Now it runs rich, black smoke at idle, no check engine light, I checked o2 sensor, iac, and did a full tune up. I also fixed an exaust leak at the manifold gaskits. And still no change! I see there are others with same type of problems with this vehicle, [any help out there?]