1998 Toyota Corolla oxygen sensor

Will a bad O2 sensor make the engine misfire badly? If so would it likely be the one before or after the converter?

I've changed the wires and plugs. All of the cylinders are firing. But while idling in gear the car is running very unstable and there's a lost of power especially when the car has ran for a period of time.

Thank you for your reply.

Ell