It looks kinda like the old Delphi/ACDelco three wire unit that we all know and love...I'm guessing that the 4th wire (green) is IAT -- won't know for certain until you chase it down.
Red - Supply/Reference voltage +5v
Black - Ground
White - MAP signal (3 bar or 4 bar)
Green - Intake Air Temp.
Edit: IE VMPSND and wiring. Red - Supply, White & Green - Gauge, Black - Ground.