A question for my friends,
The Blue Meany died about 90 seconds after taking off this morning, losing power during a shift then crapping out entirely. I fiddled with all the usual things, including disconnecting and reconnecting the wiring harness to the engine temp sensor, which I’d just fiddled with and tested that morning. Still no start. Then I fully disconnected the AMM's wiring harness and gave it a turn: it fired right up on what seemed like the first crank. I killed the engine and reattached the harness and it started again, which came noticably a little harder this time (1.5 seconds or so), and I limped her home.

Now so far in the driveway it will start just as before with a COnnected AMM, and it is unsurprisingly hard/slow. The idle dropped way down to 400 or so (that never happens) before holding at 800.

I tested the AMM for spec readings. Here's what I found:

Platinum wire resistance: 4.3 (normal range is 2.5 - 4.0)
Idle mixture potentiometer: 388 (spec is 0-1000)
Burn off fucntion: In the millivolts range I saw some numbers (0-27), and 5 seconds after killing the engine a 1 (as in, 0.001 volt) came on, then off, then on and off again. Not sure if I did this test correctly.
Heated film test: No actually didn't do this one yet (why did they put the only cold-engine test at the end of the list?)

The bigger picture: It's had truly bad mileage lately, and very slight but perceptible sputters and hesitations under load. The exhaust definitely smells of gas, but I'm not sure it never did. Inside the tailpipe is completely black although not entirely sooty. The spark plugs showed very mild carbon soot and each of them were medium-white (about half as bad as Haynes' full color spark plug guide). I replaced all 4 with spec NGK to rule out misfire. And like every 240 I've ever seen (basically mine and the ones at the parts yard), my preheat air thermostat is letting in heated air 24/7.

I am going to inspect the post-meter hoses for leaks tomorrow.

If no leaks and AMM checks out then what else on the list causes an engine die/no start then limp-home-mode? Could the culprit be as far away as the fuel supply and ignition system? And is there another way to test the AMM before I rule that one out? I want to be as specific to this particular situation as possible yet not overlook the bigger picture, if there is one (if these two are interconnected).

As always, thanks a lot fellas