Either clean or just replace the IAC, (idle air control valve), located on the throttle body, its a cylinder looking object with a two wire connector plugging into it. All fords tend to have this problem. They get all gunked up with carbon and crap and then the pintle does not move enough to allow air thru to keep the car running at cold idle. My mustang did that when I first got it, put a new IAC on it, never had another problem, along with my 91 bronco with the base 5.0. Same prob, new IAC, problem solved. If you really want, you can replace the IAC and clean out the throttle body, that will be full of carbon too.
Nick