sounds like the butterfly valve, or IAC. idle air control? yeah, if tat thing is dirty inside or u gots a leak, then it'll affect ur idling and ur gas mileage too. i remember this cos i helped replace that butterfly valve on a crown vic. if the sensor or motor is out on the butterfly valve, i think there is no part for tat. u might have to buy the whole butterfly valve. but clean it up and see if it fixes the problem first.