When engine running cold ie. warming up, the oxy. sensor has a lean biased reading but when running hot it has a rich biased reading. Should i change the oxy. sensor or could it be something else, thanks.

should be rich when its cold and about right when its hot. its becuase its in open loop mode while its cold and doesn't use the oxy. i'd say its a fuel supply problem when its cold and when its hot the oxy is over compensating.

but thats hard to say. could be both

Until the engine is seen to be at operating temperature at the temp control switch by the ecu the O2 sensor is still deemed to be in warmup mode. If the problem is the tcs after you replace it remeber to reset your ecu so it goes back to a known factory value.