trouble code 23

I have an 88 Caprice with a trouble code of 23. This is for a bad MAT (Manifold Air Temperature) sensor. This car did not come with a MAT sensor so it has to be a wiring issue. Another bonus to this engine code is it makes the car run rich and fouls the O2 sensor after about a month of driving. Any ideas?

On my '84, code 23 = Mixture Control Solenoid, but that only applies to a carbureted engine. Try checking the wired to your ECM.