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Found the answer by some trial and error
I believe the "idle mixture" adjustment may have been a major factor in my "hot soak issue". When hot, would hesitate pulling out from a stop, would sporadically run rough, lose power and stall. Fine when cold.
Checking the dwell at idle initially showed something in the range of 60-70 degrees. Which I was told indicated the O2 sensor system trying to correct for a very lean mixture. Anyway, I was looking up the correct settings and found the Bentley manual into. It said target "midpoint" of range was 43 degrees. But, even after tweaking into that range, it would sometimes seem to float up to about 54 degrees. I now know that 54 deg. is the "optimum setting".
Here's what I think was causing the "hot soak' weirdness. With the "idle midpoint" dwell angle set high (in the 60's) or low (in the 30s or 40's), things seemed to run OK most of the time. But, the O2 Sensor feedback loop was somehow "unstable" and under some conditions could not correct the mixture to give the correct O2 ratio. Being unstable, it went off to an extreme value in the 70's and could not correct itself. On occasion, revving the engine would put the dwell angle back into the correct range and all would be well for a few minutes.
I did finally hook up the dwell meter so it was inside on the dash where I could see it while driving. When things went weird, the reading was in the 60's or 70's. Wondering why the system seemed to get to about 54 degrees when left at idle for 5 minutes or so, I checked out the greenbook (Volvo manual) on the k-jet.org site. It clearly states 49-59 degrees for the idle reading. So, I tweaked on the mixture until it seemed to cover that range. And, lo and behold, the O2 system would close in on the 54 deg value in not more than a minute or two. And, it would stay there (or very close to it). When set in the 49-59 degree variation range, the idle was amazingly smooth which was another indication of the "correct setting". Set otherwise, it often seemed to be continually hunting. And there would be some "roughness" in the idle that would come and go as the O2 feedback hunted for the right value.
Anyway, my "hot soak issue" seemed to have cleared up. With the right freq valve dwell, the system is operating in a stable range. I can't make it stall, even when coming off a freeway. Also, it seems that the temperature gauge is a couple "millimeters" lower than previous. This would seem to indicate a cooler running engine which would also suggest a correct setting for the idle mixture/freq. valve dwell angle. Watching the dwell angle while driving, the value did vary rather widely from about 40 to 70 degrees. But, it did not stay there very long. It would always come back to the 49-59 deg. range pretty quickly.
DO NOT attempt this adjustment without a meter that can measure 4 cyl dwell angle or a CO meter or exhaust gas analyzer. Although, I do remember a previous mechanic many moons ago that could get the right setting just by the sound (smoothness) of the engine.
I'll try to abuse the car tomorrow during the daytime when the ambient temp is higher.
Jon
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