turboed350z

Ok so im doing little tune up and my car and im running into a few little problems. One of which is my gauge. When i start the car its reads 14.8 then bounces around for a sec or 2, then it starts increasing to 15, then 17 then it just goes blank with 3 dashes like "---"

My question is, does this sound like a sensor problem or something even more complicated? I havent driven the car since my seats STILL isnt here yet (3 months and counting 😠 )

what are your guy's opinion? Im trying to get a competent tuner to retune my car but last time it ran, it ran fine without any hiccups.