stalls when put in gear

[faof2]

1991 Volvo 240 California car automatic with about 140,000 miles.
Sudden new problem. This afternoon, in the rain, with a cold engine, I drove about one mile to run an errand. When I stopped at 1/4 mile, at the signal light on the way, the first indication was that it hesitated to get going from the stop, the way a carbureted engine might behave if it does not get enough gas. Didn't think too much about it. At my destination in about one mile, I stopped for about 15 minutes. When I returned to the car and tried to start it, it did not seem to want to catch. That is, it cranked quite a bit and had trouble staying running. When I did finally start it, the most dramatic symptom is that when I dropped it in gear, the engine quit, much like a carbureted engine acts when it is cold and needs to be choked. Specifically, I was easily able to rev the engine, then drop it in gear when it slowed down. This cause the engine to quit. Finally got going and it ran poorly at times, especially hesitating or "missing" at various speeds. Stopping at another signal light on the way back, the engine stopped when the car stopped. It started up readily, but each time, as soon as I put it in gear or gave it a little "gas", it stalled. The motorists behind me helped out by blowing their horns. That must have helped because I finally I got going and drove it home and into the driveway where it now sits. I checked under the hood hoping to find an easy explanation such as a vacuum line disconnected. Found nothing wrong. Meanwhile, no trouble codes.
Looking for ideas of what to check that could explain this new uncharacteristic performance. If I had one question, it would be " what causes the engine to stall when it is dropped into gear?"
By way of background, this car has been thriving on neglect and has been having various apparently minor performance issues. No cap, rotor, plugs, wires ( I almost said "points") for a number of years. The sudden onset of dramatic symptoms tends to make me think this is a specific "new" issue.
Before this disturbing development my plan was to eventually clean the mass airflow sensor and the throttle body, then possibly replace the plugs, cap, and rotor.

[dj_v70]

Wait for dry day and try again. If issue only happens on wet days, it is likely wires or distributor cap or other high voltage component.