Rough Starting

[MattB]

My G20 was starting hard today. It cranks normally, but when the engine comes on it doesn't smoothly rev up and drop to proper idle level but instead goes straight to the idle point rather roughly, almost sputtering. It's hard to describe, but it's a rough start. I'm thinking it's caused by a dirty IAC valve or throttle body since it happens both when the car is cold and warm. Could a bad O2 sensor also be the cause of this? No Check Engine Light...valve cover gasket and motor mounts were just changed as well.