Need to unhook the battery to reset the system. Bad gas mileage can be lots of things. Mine started going south when I got all my gremlins worked out (so I thought). Turned out the fuel feed line from the tank to the pump was pissing only when I was driving until it let go 30 miles from nowhere this weekend.
Lots of things can cause bad MPG.
Life is full of sharp turns, you better have good tires.
Its a turbo, its suppossed to sound like that!
91 940 Turbo Wagon