having vibrations in the dashboard when lightly pressing or letting off the gas

The IAC valve is controlling engine air at idle, and on deceleration. Possible issue also?

Thanks for the input. It's just for a split second when pressing the gas or letting off of it then it doesn't do it when I'm really giving it gas or letting all the way off the gas. It's like trying to maintain a certain speed (say 48 mph) with your foot on the gas and at the point of giving it gas to not giving it gas that you get the shudder or vibration. Hope that helps in describing the problem.