I'm guessing the RPM hovers at a little higher than idle when the car is stopped and in gear?
Look at the throttle body when the motor is running and car is stopped. It should look like a bit of throttle is being applied.
Did anything happen before this issue? What codes are popping up? There could be another issues that's causing the IAC to "giving it a bit of gas" or it could be a throttle body issue or it could some other issue.
What does the throttle body look like when the motor is shut off compared to when its running? What happens as soon as you start the car?