Rebuilt ECU, now low idle

[fixkick]

Short story, got my 92, geo tracker, 3sp auto, 8v, 4x4 about 3 years ago. In the 3 years iv done new timing procedure to fix the worn shaft cog per fixkick and has be great since. Recently I've developed a shudder under load, new plugs (gapped to .028) and wires about a year ago. All research lead me to the ECU, took it out and found out it was for a manual transmission. Got the right rebuilt ECU
From a FB group member. The shudder I found out was from a broken plug wire, fixed it. Put rebuilt ecu in, now (cold start) I have to keep my foot on the gas for less then a minute or it will cut out. After that minute is idles like normal at 750rpm. Could this be a problem with the ecu? 
Tried to keep it short but wanted to give as much info as possible.

cars are complex so problems go deep and long all that is normal for SURE 28 year old  cars,  very few even run at all now.
the MT ECU runs ok but TCC lockup overdrive is dead 3sp is hyramatic so only TCC is electric.,  so does the old ECU MT run ok? now?
you have 2 ECU so you can answer your own question there.

the ECU must work and operate the dashpot,  started up, the DP runs for 5 to 15 seconde cold started and retracts, does it?  2 person test, one at key one looking DP vacuum dealybob on rear of TB.  it is engaged,  key off, it holds the TV valve open  no started and for up to 15 seconds after.  that is your 1st air supply.
the 2nd air supply (of  4) is the iAC is wide open in the base of the TB this gives you 1500RPM  cold, near.  if dead , this IAC therm wax device then you the human
gets to be the IAC, ECU does nothing to the IAC<  3 on the list is hot idle iSC but only if it sticks open cold and is not your issue, and the air bleed screw.from center of TB air horn it is, you hood up fact it and it is dead center, most have plastic cap this is hot IDLE ISC duty cycle settings, (calibr) at 50% but does give some cold air cold start,  (seen some cars person with vacuum leaks , screwed the bleed closed, then later cured (hoses bad) not the bleed is set wrong.
monkey rigged.

Refurbs on this ECU is mostly caps, most parts in side are not made now. (cept caps and resistors) so super hard to fix other than caps.
I can do transistors subs but the hybrid chips are unobtainable status.
having a spare ECU on any near 3 decade car is  prime idea.  (I'd keep the MT sure would and beats a tow home say 100 miles deep in the woods.

The ecu controls ISC and DP,   that is it for RPM
and then spark advance, is the DLC number pins empty?  must be.
extra air also can be stuck in limp home, is new ECU showing 12 codes for normal this is first.  always.
in in limphome, it will flood and throttle foot adding air is the only cure,( fake cure, that is band-aid)  limphome is the #1 cause of many  of these cars getting near 15mpg,  horrid mileage and glowing red CAT, and then it melts.  code 12, a must, is it?

DTC=12 good. all others bad.