adK

Thanks for taking the time to read through the entire volume that I posted here.

Yes, the engine has a TDC sensor (behind the top section of the belt cover).
Resistance of all sparkplug cables and the coil cable are within FSM specs (25,000 ohms at 70F).

I'll mention again the engine's instant cold startup, smooth idle characteristics and its smooth operation until:
the engine speed is held at 2500-3000 rpm for 10-15 seconds
or
the car is driven a few miles
then
the idle quality degrades and throttle response softens, pre-stall. and then it always restarts, sometimes with difficulty.

I appreciate your input.
adK