VX O2 sensor reading to wide?

[VXman]

Hello, I am new here but have been getting lost of ideas and answer from here so I thought that it would be more helpful to join. I get right to the point...I bought a 92 VX about 3 months ago, when I bought it it had set for 2 years and need the trans rebuilt. So I rebuilt the trans, put on a timing belt water pump, and plugs, wires, cap and rotor. All of course made in Japan or Germany. I also installed a multimeter for the O2 sensor voltage to tell when I was in lean and also to be sure the O2 was working right.

Now here is my problem....after the car is warmed up, when I am driving in lean it reads any where from +.8 to +1.2 but when it senses load, like a small hill or something it will go straight to -1.0 to -1.2. now that is with not even pushing any more on the gas. Now this is how it runs all the time it is ether at -1.2 or at +1.2 there is no in-between, its very rich or very lean. I also have no check engine light on.

Now from reading a few other posts on their readings, it seems to me that my O2 is bad. But I wanted to get your option on this to be sure before I go out and but a $200 sensor. Could it be something else or....? thank you