8 Valve  MAP :  Manifold Absolute Pressure Sensor:  (aka: Baro sensor)
Do not get confused, there are other baro's  , the ECU has on (INSIDE) on newer cars, and one for just the EGR. This is about 8v only TBI.
Inside below is a baro chip, My guess? is piezoelectric chip and op. amp to scale the chip from 0 to 4 volts out.  It is very rugged if not dropped or crushed.

MAP sensor bolts to the engine bay firewall (Right side)
It's located on the firewall , next to the battery.
This page assumes you have tested a MAP one time before, so I will not go to extreme details. (it was just my personal journal, but now I added more...by request..)
This sensor is Absolute air pressure. so at sea-level , not running engine, you have a reading of 14psi or 29.9 Inches HG,  (the total backwards of typ.Rel. vacuum gauge.)
0 pressure is a hard vacuum and 14.7PSI , or 1 atmosphere, is max output, about  4v.
In outer space (pretend) the output will be zero. (no air, at all and zero pressure)
This device is very easy to test.

You do need a mityvac or HF hand vacuum tool and a DMM.  ( you can test on car) off car, takes a 5vdc power supply.
If no back probe needle, go to walfart and buy some leather sewing needles. (or any sewing store) (not wanting to do mail order from Pomona electronics , real probles....)

Click Here, to see my full Map sensor data , both with a volt meter and with my ODB scan tool.

The quick test for this sensor:
On Car test:   (the meter minus lead , needs to be at battery minus lug for best accuracy)
We next to the tests with the meter minus lead.  (on car test below) Key off to start.  Do not remove the side connector but do remove the vacuum line.
Be very careful and not break the plastic nipple below in photo-1, I remove the other end of hose to lower my risk here, Attach the hand vac. tool here.
Test the meter first on any battery , but 9v is best.
(use a quality meter and test the meter with a 9v radio battery for 9v reading, on the 20vdc range.)
There are only 3 pins, one is power, the other is ground and just one output pin, that measures BARO.
  1. Connect a voltmeter (or DMM set to volts)  to the center gray/green wire , "called output".  This is done by using a back probing method, with a needle.
  2. Ground the black negative lead of the meter to battery minus. 
  3. Key on, no start.
  4. Back-probe, Gray-red  (G/R) connector wire at the MAP.
  5. This Gray-red power wire must be at 5vdc (4.5 to 5.5v) or the ECU is bad.  (or the cars 5vdc power harness is cut or grounded to the body frame.
  6. Back-probe, the  Gray/Yellowground pin , it must read at 0 volts (ground) if not? , the wire to this pin is broken.
  7. With the table in mind, test the next pin (output pin)
  8. Back-probe the Gray-green pin , see about 4 vdc  just key on. (see Table for why, the voltage is high, because of earths AIR PRESSURE IS about 14PSI)
  9. Attach a vacuum tool like a MityVac or this and pump up the values shows on the tables above.
  10. Pump the handle and as you reach 15 inches, HG, the volts drop to 2volts.
  11. Then Pump to the max vacuum ,you can reach and get near 0 volts,  I got 0.5v , 1/2 volt,   The voltage pumps down.  the reading are smooth as you go.
  12. At max HG inches vacuum you are near outer space , hard vacuum.  and the MAP reads near zero.
  13. For sure a vacuum gauge is needed to do this test. and the hand pump comes with that, for free.
  14. No tools ,but just a volt meter?   Map connected up 100% and vacuum to plenum too.
  15. If you do not have a vacuum pump, then start the engine with a vacuum gauge attached, to the intake at the EVAP nipple.
  16. looking at the tables again, and testing the output pin (just see, if the MAP matches throttle actions? below..)
  17. Then, try racing engine under different conditions and try to take readings from the MAP sensor. at idle, 2500 rpm or at WOT(ashort time WOT test) wide open throttle.
  18. Key on, see 4v, @idle at 1.2v , then @2500 rpm ,see  2vdc , then @WOT bump the throttle for an instant & see the voltage hits 3.5 vdc !.  (all signs of a GOOD map)
  19. Using these techniques you can validate the MAP sensor. (even with a $3 HF junko meter)
  20. If the map is dead,  be sure to check power and ground at the pins shown below.
  21. Never ever seen a bad MAP, (clogged, line or cracked , yes, vast times , leaks on hoses) Only bad MAP seen, is from hitting it with an engine pull,  (massive damage)
  22. Pin 1 is on top. But that don't matter, I am using only colors here.

Get a DMM meter, that costs about $15 to $30, sure more.. , or it will be crap.

All tests above are with the  voltmeter black lead attached to the battery minus LUG.  True ground.