I had it running great, drove it around, had lots of power, then it stalled (at home fortunately) and wouldn't restart. I did nothing and tried it again the next day and it fired right up. It stalled again a minute later, and now it will start right up, then stall 5-10 seconds later like turning the key off without any sputtering. If I floor it when it stalls, I can often save it. I've had it running for minutes at a time doing this, and it idles erraticly and adjusting the idle screw on the throttle body doesn't do a whole lot. It has been cleaned and I replaced the O-ring on it. Holding the gas halfway will usually keep it running, but the engine pulses.

Here's what I know:

Cap, rotor, plugs, wires new
fuses good (even under the hood)
AMM tested good and set to 380 ohms (no difference when unplugged, either)
I have spark at the plugs, I pulled them all and they looked a bit damp
Timing belt new and timed properly
fuel pump works
fuel pump relay works
coil is good
fuel pressure regulator is new
all 4 injectors getting power
TPS set properly
checked thoroughly for vacuum leaks, none found
air filter ain't great, no difference when I cracked the air box open, though
Ignition timing is suspect. I set it by feel/ear because I can't find my timing light. It is set where it was running great.

I might be forgetting something, I did a lot today.

It is definitely an electrical/ignition problem. I can restart it all day, and it stalls consistently 5-10 seconds later. I can rev it with my hand and feel it switch off very distinctly. Where else should I look?

Oh yeah, it's an '85 244 B230 w/M46 169k
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1980 244 diesel M46 168k, my 4th 240