No, the mils wont have ANYTHING to do with your A/F ratio. They plug into the BACK set of o2 sensors that monitor the cats function. Wont affect anything with the a/f.
What do you mean "plugged into the rear O2 sensors"? If you are getting your gauge reading from the wires coming off the sensors (before the connectors) then it probably isn't accurate - those wires are shielded. The A/F gauge is pretty inaccurate to begin with - narrowband. You should tap the lead into the wire coming off the PCM instead. Find the pin-out diagram and tap into the signal wire for a front O2 sensor. It's not shielded, it's inside the vehicle and offers easy routing for the wire, and it's a better signal. Also, the rear O2's (after the converters) will return a different A/F ratio than the fronts (slightly). The rears measure catalyst efficiency and the front are used to manage A/F.
Youll need to tap into the grey wire with the light blue stripe on the large connector on the EEC. I just did mine today and it works great, I have home-made MIL eliminators.
That wire is bank 1 sensor 1 signal (upstream, one of the two you didnt patch).