Well I think I found the problem. Egg on my face.

The car had sat for a couple of days so I started it and pulled each plug wire in turn to see if one cylinder wasn't getting spark during the 'rough idle' period. All cylinders were getting spark.

So I decided to pull out the plugs so I could use their condition to help diagnose the continuing problem. Hoped to find one cylinder with evidence of too much 'lean', to find a possible bad injector. These are new plugs I put in last January.

Turns out 2 of the plugs were loose. While I had torqued them to spec, I guess the block was the wrong temp when I put them in, and they had loosened more since then. I mean REAL loose, like 2 turns loose. They must have vibrated and backed out slowly over time, which would account for why the condition was getting worse over time.

Of course, with 2 plugs backed out that far, the spark wouldn't be in the right spot in the combustion chamber, AND it would mess up the compression on those 2 cylinders. And once the engine had warmed up some, the cylinder would fire better even with the spark in the wrong place, and the head's expansion would tend to seal the thing up so the compression would improve. makes sense, right?

Anyways I put the plugs back in to the proper torque spec while the block was about 70 degrees F. And the car started right up without hesitation, and it started again this morning without issue. crank crank VROOM.

Bottom line: if you have an issue with starting/running that goes away after a couple of minutes, check your spark plug tightness.

cheers

Thaddeus