Fuel injected engines can't use a throttle screw like a carb had so they use an IAC(idle air control) valve to set idle, the computer controls this valve.
It is located on the upper intake manifold by the throttle, it has 3 wires and 2 bolts.
This is an electric stepper motor connected to a valve.
These can get dirty and stick, they are easy to remove and clean, just unplug the wires and remove the 2 bolts, pictures here:
http://www.explorerforum.com/forums/showthread.php?t=84220
Fuel injected engine also can't use a Choke Plate, no jets.
So computer has it's own engine temp sensor called the ECT(engine coolant temp) sensor, this is a TWO wire sensor located near thermostat.
There is also a ONE wire sender for the dash board temp gauge, these look similar but are different, remember TWO wire and ONE wire.
ECT sensors rarely fail, but not never.
How fuel injected engines start:
When you turn on the key computer starts
Computer opens IAC Valve all the way for starting engine
Computer checks engine temp via ECT sensor
You crank engine
Engine starts and(without touching gas pedal) RPMs should go up to 1,600rpms(IAC Valve is open all the way)
Computer then starts closing IAC valve to match engine temp(from ECT sensor)
If engine is cold, computer will set idle at about 1,100rpms(colder temp higher idle)
Then as engine warms up(ECT sensor) computer will start lowering idle.
When engine coolant is at 195degF(warmed up) computer will set "target warm idle" programmed in its software.
Computer for manual trans has target 600-650rpm, automatic, 750-800rpm
Now if you are not getting the high idle on cold start I would first clean the IAC valve, because it should open regardless of ECT sensor temp.
If engine has "target idle" even when cold(computer "thinks" engine is warm) then I would test or replace ECT sensor, the TWO wire sensor.
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