As with the TPS, most MAP sensors are best checked using jumpers with contact taps so the component can stay in the system. On a garden-variety GM car with a feedback carb, terminal A is ground, B is sensor output voltage, and C is reference voltage. Using a hand pump, apply vacuum to the sensor's nipple, and see that 2.3V is available at 10 in. Well, unless it's the type that extrapolates that data from the vacuum sensor and rpm signals, it reads it directly either by means of a rotating flap-type air flow meter, or a more sophisticated mass air flow sensor. The air vane rotates against spring pressure according to how much of the atmosphere the engine is ingesting, and this movement turns the shaft of a variable resistor, thus changing the signal to the computer.
Testing is simple.
Look for perfect continuity between E1 and Fc. Just as with a TPS, whether you're taking volt or ohm readings, they should change smoothly with no jumps either way. We won't get into the intricacies of mass air flow sensor testing here.