[Funracer]

Is your 35C temp switch plugged in? The switch is on the front side of the engine below the throttle body. You can reach through the fuel lines around the throttle body and feel if the wire is connected.

This switch is normally open (NO) under 35C and if unplugged (or failed open above 35C) will remain open and never close. It works with the little grey throttle enrichment switch attached near the top of the throttle body with green and brown wire. When open it adds fuel for 2 seconds every time you touch the throttle when engine temp under 35C. With each shot it throws the AFR gauge rich (lowers AFR) by 1 or 2, which is a lot. Even at cruise you are touching and releasing the throttle unconsciously to maintain a speed. It makes the gauge jump all over. You can feel the engine surge at cruise as it richens with the slightest touch of throttle.

I have unplugged mine on purpose (with O2 also unplugged) and watched and felt this surge happen. Long shot but easy to check since you have an AFR gauge.

Good luck