My car shuts off when I drive it and I took it to a mechanic. I'm not sure what he did but it hasn't shut off again. He told me if it did shut off again, that I would need a Idle Control Valve. About a few days after he fixed the car, my check engine light came on. It seems to come on after an hour of driving or if I'm driving over 40mph. It's been doing that for the pass two weeks. But I was still able to drive it. I haven't gotten it checked out yet. And now when I start the car, the check engine light comes on immediately and the car feels like it's shaking/vibrating a little.

What does a Idle Control Valve do? And how much does this part cost? I haven't taken the car in to be checked because I'm looking for a new mechanic. I don't really trust this guy.

Idle air control valve will run about $450.00 thru the dealer. It adjusts the idle of the engine to prevent stalling.