First things to clean would be the MAF(mass air flow) sensor, and the IAC(idle air control) Valve.
Ford MAF sensor uses a heated wire, as air flows by the wire it is cooled off, this cooling off is measured and computer can calculate the weight of the air coming into the engine, and from that computer can calculate the 14.7:1 air:fuel ratio.
Over time the heated wire can get a coating on it, so data the computer is using is off a bit.
You clean this wire using electronic spray cleaner, NOT carb cleaner or similar, you can also get MAF cleaner at auto parts stores.
You should clean MAF sensor every few years.
Read here: http://www.therangerstation.com/tech...CleanMAF.shtml
MAF sensors were changed from 4 wire to 6 wire in mid-1990's, MAF sensor didn't change but an Intake Air Temp(IAT) sensor was added, thats the extra 2 wires.
Fuel injected engines have no Jets like a carb engine did, so air flow changes doesn't suck more or less fuel into engine, and so an idle screw won't work, neither will a Choke Plate.
IAC valve is located on an air passage bypassing the throttle plate, it is controlled by the computer.
Computer opens the valve more to raise idle, and closes it more to lower idle, and computer adds or reduces fuel via the fuel injectors accordingly.
When key is off IAC valve will be closed all the way, when key is first turned on computer will start up and open IAC Valve all the way for starting.
That's why warm or cold the engine RPMs should go high just after starting and then drop as computer closes IAC valve to set idle according to engine temp, higher cold, lower warm.
IAC is a mechanical valve, it slides inside a tube, so it can stick if it gets dirty, this can cause RPM issues as computer ties to unstick it when RPMs are too high or too low.
This is a general IAC Valve cleaning procedure: http://www.rangerforum.com/threads/h...3-engine.4972/
And here: http://www.explorerforum.com/forums/...ad.php?t=84220