1995 vw golf 2.0 check engine light

I have a 1995 vw golf 2.0 gas man trans. when i accelerate through gears the check engine light comes on around 2500 rpms and turns off around 3500 or if i let off the gas. it has new plugs wires but im wondering if its 02 sensor or other sensor because it doesnt happen when i disconnect battery and reconnect. it happens about a day after that again though once the computer runs diognostics. please help