201 is definately O2 sensor control. Bear in mind that the temperature sensor sends messages to the DME so that it can set appropriate fuel trim values according to engine temp. (i.e. cold engine = rich mixture, warm engine = lean mixture etc). If the engine temp sensor thinks the engine is cold when it is actually warm, the DME will enrichen the mixture but the O2 sensor will detect that the mix is too rich and attempt to lean it out. In other words, the DME will receive conflicting messages from the O2 and temperature sensors. In light of the effort you have put in up until now, I would tend to bite the bullet and change the temperature sensor (the one on the side of the cylinder head, not the one on the radiator).