My 92 model 240 has been throwing the Computer code 1-2-1...."Mass air flow meter signal faulty or missing".

That is the only code that's it's storing.

I have changed out the Air Mass Meter with (2) known good meters, and the same thing keeps happening.

I reset the computer, change the Meter and this happens
The engine will start, idle very roughly and hesitate on revving.
If I rev past 2000 RPMS, the engine will clear up and run strong.
After about 5 minutes, the check engine light will illuminate, the car won't idle and runs rough.
Code 1-2-1 every time...and that's all.

The engine will still run strong above 2000RPM.

Any idea if there is another combination of faults that can trigger this code?
I've got a hunch that the throttle position sensor may play a part.

Unfortunately I have my wife's 94 model 940 in my shop with the heater hoses removed (on order), and the temperatures have been in the upper teens to the low 20's for the last few days, and I'm too old to shade tree anymore.

Any idea is appreciated.