Correct me if Im wrong, but isnt the map sensor supposed to read the same as the barometer(key on engine off)?
My 97 Z28(boltons stock cam) reads 26.0 while the barometer reads 29.1

 

Yes, the MAP sensor is used by the PCM to measure barometric pressure before the engine starts. It would only read 26.0"Hg if you lived in Denver or similar elevation.

 

The MAP reads uncorrected, absolute pressure--commonly refered to as "Station Pressure." The Barometric pressure your barometer or the weatherman reads is usually corrected for elevation. This makes it much more useful in predicting the weather--but quite useless at telling your engine how much fuel it will need.

 

Cool, I get it now, I connected my scanner to a few other cars and they all read the same thing.
Thanx for the help.