Ok so my check engine light has been on for about 5 months now. Apparently my car is running to rich. I get a code 45 when I do the paper clip trick. I took it to autozone and had them hook up a scanner and the worker told me that the engine is running rich. In the past few months, I have changed my gas filter, spark plugs, distributor cap and rotor, cat-back, and air filter. Could it be the oxygen sensor? Does anyone know what the problem might be?

Oh and I checked my spark plug wires with a multimeter and they are within spec.