I learned this after a former student had this problem with his Taurus. I never taught my kids to measure sensors except to verify that they found the cause of the problem and to learn how the circuits work, but in this case a resistance reading showed the value to be bouncing all over the place. That is extremely unexpected since temperature sensors have only one part inside. That is a temperature-dependent resistor, known as a "thermister". I have to guess there was a mechanical break in the resistor or one of the wires attached to it. After I mentioned that to a friend who worked at a Ford dealership, he just shrugged his shoulders and said they ran into that very often. For that reason, suspect that sensor first before looking for other causes of your idle speed problem.
If you have a temperature gauge on the dash, you should have two coolant temperature sensors. The gauge uses a sensor with a single wire. You want to look for the Engine Computer's sensor which uses two wires.
If the CTS doesn't solve the problem, you'll need a scanner to view live data to see what the computer is seeing when it reacts by raising idle speed. You'll also be able to see if the computer is actually requesting that higher idle. If it is not, suspect a vacuum leak. That will cause a high idle speed without a corresponding increase in power.
Tuesday, March 15th, 2016 AT 4:09 PM