The MAP on a STI is a 2.8 bar from what we know about them, Make sure you are tapped into the map sensor for one. One wire should show zero volts at idle, the other 5v and the other around 1.2 volts which will increase if you give it a rev because the vac till go up.
A good place to check is the PCM pin out and make sure it's going back to that sensor. On the WRX the output source is B8. At least on the information we know about it.
2002 WRX ECU Pinouts