Idle Motor - Idle Air Control Valve. (IACV)
That would have no effect on your shaking or lack of power off the line. It only controls your idle speed.
Do you have a check engine light on? Does the light work? (comes on when the key is turned to the on position)
Your shaking indicates a week or misfiring cylinder. What kind of spark plugs are in the car and when was the last time they were changed or inspected? You should only run NGK Platinum tip plugs. They are expensive, but last for 60K miles. If somebody put regular plugs in your car, they probably have been burnt up by now. That would account for your poor idle and lack of power.
Other things to check for is a dirty throttle body -
www.motorvate.ca has a nice write up on how to clean this yourself. (5 bucks for a can of cleaner) Defective PCV valve (under 10 bucks at any auto parts store) or a dirty fuel filter or injectors.
I'd check the plugs first. Perhaps another mechanic is in order as well.