Before Electronic Engine Control (EEC) systems with electronic fuel injection were installed on cars, the function of allowing a car with a cold engine to start and idle properly was performed by a mechanical choke. This was a butterfly valve located inside the carburetor that closed off a portion of the air flow to the engine while leaving the fuel flow the same. This richens the Air/Fuel ratio enough to allow a cold engine to idle smoothly until the engine warms up and the choke gradually returns to full open.
Cars with EEC systems and electronic fuel injection don't have a carburetor and therefore don't have a choke. What they do have is a sensor located in the coolant lines on the engine that reads the current temperature of the coolant circulating through the engine and reports that reading to the EEC computer.
On most Fords that sensor is called the Engine Coolant Temperature (ECT) sensor. If your ECT is electrically out of range (effectively busted!) it can no longer report the correct engine temperature to the EEC computer. And, therefore, the EEC computer can no longer send a signal to the fuel injectors to stay open longer on each fuel injection pulse to richen the A/F ratio because the engine is sill cold.
So, if your engine does not idle correctly with a cold engine but idles fine once warmed up, the most likely culprit is a bad ECT sensor! Go to the Ford parts counter and buy one for your particular engine and install it. (About $35.00 or so.)
If you don't want to pay the $35.00 without knowing for sure that your ECT is out of range, then go to the local book store and buy a copy of Ford Fuel Injection & Electronic Engine Control, 1988 to 1993, by Charles Probst (covers all Ford EEC IV systems, not the newer EEC V). Read that book and learn how to run the computer Quick Checks on your car. The quick checks allow you to read the trouble codes that are stored in the EEC IV computer. If your ECT is out of range, the trouble code for a bad ECT will be output when you run those checks. You don't need to go out a buy a fancy STAR tester to read the trouble codes (though its easier). You can read them out directly from the flashes on the check engine trouble light (MIL) on the dash board of your car. If you are going to do your own maintenance on a Ford with and EEC system, you owe it to yourself to learn how to do this. It will save you hundreds of dollars at the Ford dealer if you do.
PS) There is another temperature sensor that can affect engine performance, thought it does not have anywhere near as much effect on engine idle as the ECT. This one is the Air Charge Temperature (ACT) sensor. It is usually located in the inlet air path ducts coming into the upper intake manifold before the throttle body. It senses the ambient temperature of the outside air coming into the intake manifold and reports that to the EEC computer. The EEC computer adjusts the A/F mixture accordingly. If you don't seem to have quite the right A/F mixture at part to full throttle (engine surges or runs lean/rich) the ACT may be to blame.
There are a dozen or so sensors that send various signals to the EEC computer so that it can control your engine correctly. These are just the two that have to do with operating temperatures.
Good luck with your troubleshooting and repair.