Thanks Dom.
I did continuity check all the wires in question, All others I added I had checked at the time of installation.
The factory IACV arrievd late this afternoon, so I plugged it in & ran the diagnostic checks again - this time everything passed - the main one was that with the key on, I didn't have vBat between A12 (signal wire at IACV) and ground. With the new one, I have the correct value.
I installed the valve and started the engine. Idle was elevated as it should be for cold motor, and gradually dropped as it warmed up. Motor revved just fine without any funky business. YAY!!!!
So, the bad valve was indeed the cause of all my woes.
Just have to tidy up my wiring again
Time to move on to other things...
Modified the stock crank splash guard to fit - reshaped it out & away from the crank pulley.
Made a protector plate for the fuel lines & filter, rad hoses and other bits from a Volvo splash guard..
bolts to stock fuel pump splash guard plate, and to the hole in the other tank strap. Plastic-welded a separate piece back on the end for that.
Had a couple drops of AF on the tarp under the forward engine area - so went looking for the source. Found that the Oetiker on the heater hose didn't grab properly on the backside, I could feel it 'bumped' out
looking at the clamp - you can see it's not riding up over the hose at the back
Removed the clamp & found a narrow Norma-style clamp, seems to be good now
No bump out now. I've had trouble getting all the air out of the system, this could certainly have been why
Also found that the vacuum line to the heater valve had pulled off at some point in my back & forth in the bay. I repositioned the fuel return line that had moved out & reattached the vacuum to the valve
Took it out & drove it pretty hard for a short run