What would cause an '01 sienna to spontaneously accelerate?

Step father took his toyota sienna to the shop because it spontaneously accelerates. He has to put it in neutral to stop sometimes. The mechanic said (I'm qouting this 3rd hand) it needs an Air Idle Control valve and a Mass Fuel Sensor - quoted @ 500$. I'm pretty sure he's talking about a mass Airflow Sensor, but step father swears it was mass fuel. never heard of one of those. Anyway, Does that sound like the cure in any case?