This 89 740 GL wagon has 315,000 miles, ran fine, although for the last 6 months gas mileage had dropped from a very consistent 29 to 22 or 23 MPG. Then a couple of weeks ago it died and wouldn't restart. New plugs, wires, dist. cap & rotor, timing belt & tensioner, air cleaner element, now it starts with great difficulty and runs, but I think it's in limp-home mode. It doesn't have the power to back up the fairly steep driveway. The code showing is 1-2-3, so I replaced the back ECT sensor. Still no power and difficult start. Checked the voltage at that sensor's wires with the key on and engine off. Both have 5V. Should both of them have that? Shouldn't one be the ground, and read no volts?