Ford focus stoping at idling every time what problem

Restricted air flow. Replace the air filter if dirty. Clean the throttle body and MAF sensor. I use brake clean. Use a tooth brush on the throttle body , just spray down the MAF sensor. Leave the MAF off, start the car and spray some in the throttle as you rev it up. If the engine light comes on, it is because of the MAF being off. It will go out in a day or two. Or you can have it cleared.