disconnect the vac line from the map sensor , does it goto 0, if not check the votage on the signal wire , if you suck on the the map sensor does the voltage rise/fall. sounds like an issue of the signal voltage from the map sensor. connect the gauge directly to the batt and make sure it calibrates. does it read 0. suck on the map sesor , does it read vac then return to 0? let me know the results