Update to my post below re: my '92 240 and info for others w/ similar problem:

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I checked w/ ALLDATADIY and found a 1994 TSB for 1993 240's poor idle/drivability problems (probably applies to other years but I am subscribed to ALLDATA for my '93). Says that problem is exaccerbated by low volatility fuels used from May to Sept in mid temperature ranges (60 - 85 F), especially in southern climes. Describes condition exactly. There may be other contributing factors, such as PCV and throttle body, as well as infamous deposits on intake valves and/or injector and seal issues. There was a diagnostic flow chart. Top remedy listed was replacing $25 shiftlock relay and its $2 holding clip (maybe old one clamped too tight in wrong place, or maybe Volvo had a bunch of clips to get rid of). Other more expensive possible fixes included replacing LH wiring harness and replacing EPROM. I'll be putting in a new relay today and see how that works. (Will also be trying another gas brand as well as some Techron, but not until see impact of relay for a few days).