Car idles badly and shudders while driving until warmed up

When car is first turned on and engine is cold it idles badly from 1RPM to nearly stalling point (does stall sometimes) if I try to drive it like this it will shudder violently along pulling back as I try to accelerate and the engine light will flick on and off. Once the engine is warmed up the shuddering and engine light goes away however it still idles badly.
It has been suggested to me that the problem could either be the oxygen sensor or the IAC valve? Is this reliable advice?