Adbarrett,
Smitty is tellin' you the deal with the vaccum leaks. They could be just about anywhere there is an old rubber or plastic hose -with some cracks, pin holes, or frayed ends. You just need to slowly check everything over with a careful eye. Replace anything that looks shadey.
No, you cant use the o2 sensor from your 83 on a 90. FCP Groton (fcpgroton.com) is an internet import store, w/ excellent prices and good service, that will give you the best price on whatever you may need.
You still, however, can not over look other variables. When was the last complete tune up (plugs/cap & rotor/wires/ fuel, oil, & air filters) done on the car? My suggestion would be to buy a copy of a Haynes or Bently service manual and use it to stay informed (ie. before or after you see a mechanic) or to help you fix the car yourself. There are alot of things that can lead to poor economy and you need to eliminate each one by its "heaftyness" on the wallet. Peace, Jon

Adbarrett,
The 2-3-2 fault code signifies that the fuel system is compensating for a rich or lean air/fuel mixture at idle. This could be the result of several things... the oxygen sensor could be bad, there could be a vaccum leak(s) somewhere, or maybe the temperature sender is faulty. I would begin with the simple and cheap fixes (leaks) and move gradually to the more expensive (o2 sensor). As well, everything depends on how well you maintain your ride. Peace, Jon