Toyota Repair: 92 pickup running rich, egr flow, starter relay

Question
'92 V6, couple of months ago began stalling periodically and would start right back up. happened while driving or when at a stop when it began it could go 2 or 3 weeks between stalling. 5 or 6 weeks ago on a drive home it stalled at all stops, as soon as i started to slow. believed it to be the maf and replaced it. began doing it again after about 6 miles, when it was warm. checked fuel pressure about 32-34 psi and was told it should be 38-42, so i replaced the fuel pump.  it still did it, replaced all plug, wires, cap, rotor, and cleaned k&n open element filter. it still stalled so i swapped the efi relay with the starter relay and it still stalled. i took it to a toyota dealer, they replaced the open circuit relay and said if it continues it will need ecu.  it ran fine for 2 weeks, then a couple of days ago it died, and when i restarted it, it wouldn't stay running. it's a manual, and i had to rev it and throw it in 1st to keep it running. i got it home and it was putting out black smoke like it was dumping fuel. i replaced the ecu but the problem was still there. it also idles rough now, obviously with as much fuel as it seems to be dumping. the ecu is from a junkyard but since it has the exact same problem, it seems not to be the problem. the check engine light does not come on when it is running rich at idle. does it need to run a certain amount of time to set the light? also where is the open circuit relay? Thank you.

Answer
The only thing I can think of other than some sort of wiring problem that is making the ecu go to a full rich condition is that the egr valve may be sticking in the open position, this will cause a rough idle and rich running condition and this can be intermittent, before replacing the egr valve try to block the egr flow into the intake chamber by removing the valve and then use the gasket between the manifold and the egr valve as a template to make a thin block off plate, install the block off and the valve back on and see if the problem goes away or stays the same, if it stays then you can eliminate the egr system as the cause and I would start looking at the wiring harness for a problem, it may be a bad or loose computer ground connection either inside under the left and right kick panels or the ground connections at the right bank cylinder head just behind the valve cover. rear