The idle valve is located between the engine and the air filter, following the tube where the engine aspires the air, you will find the gas butterfly and the idle valve.
If you are not seasoned in the issue of mechanics, it is best to take the car to a workshop.
Another thing that you can have bad is that you have a ignition failure in a cylinder, as the partner says, or the engine with excessively low idle, or that the converter carries an oil that is not adequate and that is why it makes the engine heating when putting a speed.
I have several questions:
if you accelerate a little, the windstar comes out or do you also stop speeding? And if you accelerate in the dead man, it fails and tends to stop? or on the contrary it accelerates without problems?
Greetings and what is you tell me ok?