Thanks all for your insights.

Tonight I tried squirting propane around the intake manifold with no change - it was difficult due to the motion of the engine. I should mention the motor mounts are very bad, I have the replacements - just haven't gotten to them. However this also makes me wonder about other potential wiring issues caused by vibrations.

I also did the voltage checks using Art's graph. This was revealing:

I measured temp of the thermostat housing using an infrared thermometer as a point of reference.

thermostat housing 33C, pin 13 measured 0.6 mv
warmed up engine for a few min
Thermostat housing 43.6C, pin 13 measured 0.6 mv; resistance 746 ohms

I didn't think to check resistance in the first reading (33C), took resistance at second since the voltage had not changed. Note also it was extremely low, assuming the graph is volts, mine was 0.6 mv, 0.0006 volts.

Since the ect is new, I'm suspicious of the wiring. Though could also be a bad ect out of the box, that seems unlikely.

Any value in checking resistance from ecu pin 13 to ignition ecu pin 2? I don't know the internals of the ect.

I'll follow up on the 951s tomorrow.

Thanks

Mike