Awhile back I had alot of problems with my 1991 Firebird 3.1l V6. It started when I changed the spark plugs and then everything went wrong. Fuel mixture was off, car was burning way too rich, and running all around pretty rough.

But the SES light code that I got was Oxygen sensor too lean. We determined that the O2 sensor was bad, and was saying that the fuel mixture was too lean, even though it wasn't, so it was making it too rich.

Since then, I have changed spark plugs/wires/cap/rotor, fixed 2 vaccuum leaks, changed the O2 sensor, and cleaned the EGR valve.

The car was running pretty much the same, and I am getting bad gas mileage, but the SES light finally came on, and now Im getting code 45. Oxygen sensor rich.

So... where do I start? I've done work on cars. Tune-ups, brakes, fixed leaks, changed a radiator, things like that. But assume that I know nothing aout this, and tell me what to check first and how. I just lost my job and can't afford to take the car to a mechanic.