Thanks for the thorough reply. I long ago removed the preheat hoses from my Volvos, and usually tho' not sure on this car, remove the thermostat in the air box and block the flap to the cold air position.
I an pretty convinced it is not the AMM, although I could try the one from my '93 245 to be sure.
I checked the fuel pressure yesterday, 38psi, bumps up when opening the throttle, so the FPR seems to be OK. Stays up on engine shut down.

To be clear, the car starts fine, but within a few minutes, runs awful. Not just, need a tuneup awful, but stumbling, will not respond to the throttle, may even stall awful. Then, like a switch is thrown, will run fine, normal acceleration, nice idle (for a 200K mile engine), then it could instantly, go back to awful. It can switch back and forth in seconds, or run good or bad for many minutes.

I have changed the white pump/system relay, new one installed. Whacked it a few times, but does not seem to be it or the wiring nearby.
Changed the ECU, no difference. It has a .....951.

Pulled 2 of the plugs. both had tan at the tips, but also some soot around the bases. At that time the car was running OK. But it makes me think it is running too rich when it is acting up, although that seems incongruous with its penchant to stall.

All together, I think it must be an electrical connection problem with the way it comes and goes so fast. But I can't get a handle on what exactly is making the engine run so bad. The ECU us fine, (the O2 sensor is old, and I think one of the codes is for O2 sensor, but it makes no difference whether it is connected or not, and from my past experience, it has very little effect on engine performance or idle). it's not the AMM (unless it's the connector, will check that). May have to hook a scope to the injectors and look at the length of injector pulses. Is the ECU getting erroneous inputs, or ??

I hope I can fix this, it will make my day.
Now back to the brakes on the daughters S40....
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93 245 Classic, M47, IPD, 91 245SE AW70, 89 745, M46, IPD, Dependents-00 S/V 40s