Just purchased 1989 Reatta with 130K miles. Car runs fine, gauges show car is running fine, oil pressure 55, battery 13.5, temp 180-195. When you go into diagnostics, every system says low or problems. (Example, I just had oil changed, but it says oil is low. Fuel says low, with 3/4 tank showing on inst.panel. Temp is cool, but diag. says it's overheated...) Please advise.