Most likely the Engine Computer lost its memory and has to relearn "minimum throttle". That's Chrysler's terminology but the idea is the same. To cause the relearn to take place on their cars involves driving at highway speed with the engine warmed up, then coasting for at least seven seconds. It's real simple. I don't know what it takes on Fords for that relearn to take place but it does not involve replacing parts so don't start down that disastrous path. Usually just driving the car will clear up the low idle, but you'll have to keep one foot on the brake and one on the gas until it does.