Well, it's not the coolant sensor. I replaced that today.

To summarize:
-Misfire between 500 and 3000 RPM
-No excess smoke from exhaust
-Duty Cycle fluctuating at 50%
-New OVP, coil, cap, rotor, ICV, wires
-Only misfires when engine warm
-Hesitation on acceleration
-No difference with EHA or O2 disconnected

It looks more and more like a vacuum leak, no?
I'll look into that and then I guess I will wait until my used AFM unit with EHA and fuel distributor arrive and I can scratch that. Any other advice for now?

Tried something else
 

Yesterday I replaced the main three vacuum hoses. No improvement.

Today I disconnected the air flow potentiometer (hereafter refered to as AFP) and saw no difference in engine operation. Then I measured voltage from pin two to ground and got a fluctuating ~0.799V to ~0.810V reading. I understand this is too high. Should I try to adjust this or is it close enough? If I do adjust it how do I do it? This has been covered on the board before but I'm a bit confused. I'd like to thank everyone who has so far helped me on this.

I'm going to list what I've replaced or checked since I bought the car (in February):

New:
OVP
Idle Control Valve
Cap, Rotor, Wires, Plugs (H9DC), Coil
Vacuum hoses

Checked:
1) Compression ~11.5 bar on all cyllinders with insignificant varience between cylinders
2) Two prong temperature sensor (not four prong or one prong) ~ 324 ohm hot
3) AFP ~ 0.799V - 0.810V this is with engine on
4) Duty cycle ~ 50.4%-54.8%
5) Engine runs the same with EHA unplugged

Symptoms:
Car runs fine when cold
Misfires, sometimes backfires through the intake when accelerated hard
Starts fine cold or hot
No problems at all above 3500RPM
Severe hesitation at low RPM
Never stalls
Idle steady at 650 in N and 500 in D
Misfire remains regardless of mixture setting

I have a used AFM assembly on the way including fuel distributor.

Any advice?

Just a shot in the dark. Check your plug wires end to end with a VOM. They should read 1KOhm when cold. Wait til they are hot and check again. The Spec for the wires is 800 Ohm to 1.3KOhm. I have found that Bosch wires no longer fall into this spec when hot. Mine tested at 1.4KOhm or higher when hot and 1.2KOhm when cold. I went through many sets of end connectors and wires before I got fed up and ordered NGK wires. Which I will add tested at 980Ohms when new. Every other set I had all tested at 1.1-1.2 When new and cold. Beru and Bosch. Next that AFP can be adjusted and should read around .750 if I recall correctly. You loosen the four screws and the one side of it will slide up and down for adjustment. You can also remove it and check for wear.

You could also do the 1/8-1/4 adjustment on the EHA as well to see if that helps at all. Some say it helps some say it does not. I will tell you know that it helped on my M102. By adjusting it I get better off the line performance as well as better high end when floored. You will have to re-adjust your base mixture setting after doing this adjustment. To enrichen mixture you go clockwise and to lean of course is counter clockwise. This makes up for a worn fuel distributor.