It's built into the ECU, so you'd have to get a new one if that's the problem (though I doubt it is). Disconnect everything, including the MAP sensor, and test the voltages on each wire with reference to chassis ground (meaning put the negative multimeter lead on either the battery or a clean metal part of the chassis). You should see +5V on the Vref line and 0V on the ground line if everything is as it should be.

If that checks out, you'll know the problem is with the FCD or the MAP sensor. If not, then you'll know the problem is likely in the stock wiring or the ECU.