i'd have to agree with looking for air leaks, also idle control vales are noutorious for causing irractic idles, as this happened on my omega. best way to tell if theres a fault with your oxygen sensor is to take it to a garage and ask them to check the emmisions for you, as this will then give you a definitive answer, also are there any leaks in the exhaust system as this can cause uneven idle
Cheers
Shaun