I read through most all the associated threads on this subject, and there are many. I didn't want to start a redundant thread but I think I've done most of what I can find. But apparently I'm missing something because otherwise it would be running. hopefully someone can read through this and see what I've missed.

I have an 88 XJ Waggy 4.0L auto that has a super rough, rich idle. It stumbles and then dies. Seems to run well at higher RPMs. I have access to several parts vehicles plus a couple more that run so I can get data and parts from them. I have done the following, replacing the items with ones I know to be good from previous projects and current running vehicles: I have a very good running 89 4.0L that I put readings on the attached chart for comparison.

New Champion plugs. High quality US made cap and rotor, brass connectors, new 8mm plug wires.
Compression test, 120lbs (+)- 3lbs all the way across, all the plugs looked the same on all 6 cylinders, normal but fuel soaked. 52lbs fuel pressure at the rail (not positive that gauge is completely accurate, but its same pressure as the 89)
Refreshed the grounds to the block at the dipstick, cleaned that area and all the fittings/ cleaned the 101 firewall connector
New 2ga ground cable, new 4 ga ground from firewall to rear of the head.
Swapped the following known good sensors: CPS/TPS/IAC/MAP/ O2 Sens(new NTK)/ECU from 89
Cleaned the throttle body. Put a manual vacuum on the EGR to see if it made any change. the valve was operable, but made no change in the idle.
Found a plugged vacuum line between the intake manifold and the rear fitting on the valve cover, cleaned that out, no change.
MAP sensor line looks good, not plugged, does affect the idle.
Noticed this unit has Canadian spec sticker on the firewall, Cat has been removed.

I am not getting 12v to the O2 sensor, only the 5v on the other wire. Swapped relays to make sure that was not the problem, no change. However the 89 that runs like a champ has no voltage to the O2 sensor either. I took the O2 relay out and straight wired the O2 sensor to give 12v to the sensor, made no difference. *** O2 voltage on the poor running 88 is not on the attached chart, it is 1.25-1.50v

Attached are the readings from the Brick, IDK if that can shed any light on the subject. Any ideas would be appreciated. I've had several Renix 4.0's over the years, I've never had a problem like this I couldn't figure out.