i spoke to a mechanic who stated that removing the rear lambda is a good way of checking whether the cat is buggered, if she runs better with a bit more performance then u know where the fault lies as the rear lambda gives out a .45 reference voltage to the ecu when unplugged
now i did this when the cat was warm and got a bit more performance sepcially up rev range, when she was stone cold unplugged the fault occured
i gonn have to sticky my dissertation on my experience