Outer Limits 4x4 Board

My Vit seems to stutter or shudder at about 2300 rpm. It happens when my foot is at about 1/3 throttle. But goes away when I take my foot off or press it down full.

I have an air fuel ratio meter in the car, and I can see the mixture going normal, none (i.e. when the engine is at vacuum), normal, none really fast, coinciding with the shuddering.

Hopefully that makes sense
I am thinking it could be the O2 sensor playing up, but it doesn't make sense as to why it is happening at certain revs or throttle.

Any ideas?

mine is playing up the same way aswell will tell you when i find out wat it is

Btw, does anyone know if you can connect the existing four wire O2 sensor to a standard single wire one?

I know that the four wire ones on the Vit, have a heater in them to get them up to temp faster, but there is still only one signal out, so I am wondering if I can just connect that to another single wire O2 sensor I have, and see if that sorts the problem out.