Plugged in one of our box stock LMM trucks due to the P0101. Confirmed MAF and air filter are not at issue. However, I am seeing odd readings for MAP and Baro that do not gel with reality.

Current actual Baro conditions are 14.83psi absolute. Truck Baro sensor is at 14.1PSI, MAP boost pressure right now is -2.30 psi with truck NOT running. Obviously that is gauge pressure but that value should be zero, should it not? I removed the MAP and put finger pressure over the port hole to induce a bit of air pressure and it does respond, but no way we have negative pressure with truck not running! I am trying to figure out HOW that MAP value is being calculated to arrive at -2.3PSI because it should just compare whatever value the Baro is spitting out to the intake pressure. ?

I mean, I would think the Baro value is probably close enough to run, but I have issue with the MAP reading.