ECU for a 7afe in a 5sfe 1996 manual celica Options

[thebestofall007]

Hello all, I found a surprise in my 1996 Celica: It has an ECU for a 7afe manual transmission engine, however, mine is a 5sfe manual. The engine runs well, but gas mileage is not as good as it is supposed to despite replacing the cap, rotor, plugs, wires, and I get a P0141 code despite replacing the O2 sensor with an OEM Denso and checking the wiring connection between the sensor and the computer. The cables don't appear to be all spliced up, either.

Why would someone do this, and what would I have to do to replace it with the original (if this would fix the gas mileage and sensor issues)?

This post has been edited by thebestofall007: Oct 21, 2016 - 5:00 PM

[thebestofall007]

I just noticed something regarding the P0141 code I get that may point to my need for another ECU. I got the OBD dongle and used it with scantool and the code is saying that it is related to an O2 sensor heater malfunction, but the O2 sensors in my car DON'T HAVE A HEATER. They are the 2 wire type, and not the 4 wire that has one, so I have a suspicion that the computer expects them to be there, and they aren't, and that's why the code is being thrown despite getting the Denso sensor.