Symptoms are as follows :
Car running rich, blowing black smoke, bad fuel mileage.
When cold, car runs well blowing black smoke lightly.
When warm, idle is lumpy and drops to about 600rpm.Hesitating severly on acceleration and blowing lots of black smoke.
Symptoms are the same with the EHA on or off.
Had a similar problem, same symptoms and solved it about 2 months ago by replacing used fuel distributor and fuel pressure regulator.
Background on last repair :
Same symptoms as above.
Swapped out FPR with a used one.
Car ran fine on the highway for 20 minutes and then suddenly back to rich running.
Swapped out FD and also FPR again (both used units).
Don't think the fuel distributor has gone bad, looks like a screwy fuel pressure regulator.May have been the FPR all along but don't know for sure coz both the FD and FPR were swapped at the same time.
I can see traces of fuel leaking from the nipple of the vent hose on the FPR that is now in the car.
If I understand correctly, a bad fuel pressure regulator can have an effect on fuel delivery (fuel mileage) - rich running condition.
Another interesting symptom was that after I had the FD and FPR swapped (the old FPR was leaking fuel), the car had a slight problem with cold starts.
1st key, it fires and then dies.
2nd key, it fires, lumpy idle for 3 to 4 seconds, then catches and idles fine.
The new used one is now also leaking fuel, though I did not check if it was leaking when I first swapped it in 2 months ago.
Maybe, swapping out the FD the last time was unnecessary...
Meanwhile, in Gotham City...