What would cause it to idle rough - 2002 Ford Explorer

Clean Throttle Body (both sides, not just what you can see) and MAF (mass air flow sensor) [spray and shake to dry].

https://www.google.com/search?q=2001+Ford+Focus.+running+rough+and+power+surges
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https://www.youtube.com/watch?v=bDCaAZedVYY

Rough idling can also be caused by clogged filters. ... Bad spark plugs, bad spark plug wires and a bad distributor cap are other common causes of rough idling. These items are all important parts of what keeps a vehicle running. Spark plugs provide the spark that ignites the air and fuel mixture within the cylinders.
https://takeit2thehouse.com/common-causes-of-a-rough-idling-engine/

Have you cleaned the throttle body bore and plate of carbon/deposits ? This can cause idle and off idle symptoms .

Worn valve guides allow oil to drain into the cylinders, causes blue smoke, fouled plugs will idle rough.
Coolant in the cylinders from a blown head gasket will cause white smoke.

ZULFIQARDR HAS A TOYOTA CAMRY CAR, SOUND LIKE ROUGH IDLING COULD BE CAUSED BY WEAK FUEL PUMP,DIRTY FUEL INJECTORS, FOUL OUT SPARK PLUGS CAUSED BY LEAKING FUEL INJECTORS,LOW IDLE SPEED, CHECK IDLE SPEED CONTROL COULD BE TOO LOW ARE FAULTY LOOK FOR VACUUM LEAKS ON INTAKE MANIFOLD.BAD LEAKING ENGINE VALVES.

Generally, the problem is in the emissions or something that is affecting the effectiveness of the emissions, but other causes can trigger the light to come on, too. To determine the cause, the vehicle will need to be taken to AutoZone or a shop that has an OBD2 scanner, or for 1995 and earlier models, an OBD1 scanner, While a scanner will not give you the magic answer, it will give you a code that narrows down the problem area.
Some specific causes for the light to be on are:
Gas cap left off, not tightened, not installed correctly, or needs to be replaced.
02 sensor.
Engine misfire - error might clear itself after 3 complete warm-up cycles; not restarts, but warm-ups.
At start up for a bulb check - Should not stay on.
Details here: http://www.chinasinoy.com/service/why-would-a-check-engine-light-be-on-62.html

Car rough idling causes
misfiring engine is among the most common causes of a rough idle. You may notice your car idling roughly when it's in "Park" or when you're driving it and stop at a stoplight. A rough idle can be caused by damaged spark plugs or spark plug wires or a burned-out valve. It's important to address the cause as soon as possible to avoid potentially damaging the engine. Engine repairs are almost always expensive.
Learn more here:
http://www.chinasinoy.com/service/car-rough-idling-causes-and-how-to-fix-it-108.html

Hope this helpful.
Best regards.

ROUGH IDLING CAN BE CAUSE BY MANY THINGS.I AM LOOKING AT LEAKING VACUUM HOSES OR INTAKE MANIFOLD GASKET LEAK.DIRTY FUEL INJECTORS AND WORN ENGINE VALVES WILL CAUSE ROUGH IDLING.ALSO LOW IDLE SPEED CAUSE ENGINE TO RUN ROUGH.

ROUGH IDLING CAN BE CAUSED BY VACUUM LEAKS.LIKE THE INTAKE MANIFOLD GASKET.OR VACUUM LEAKS FROM HOSES.LOW COMPRESSION CYLINDERS WITH BAD VALVES.LEAKING EGR VALVE GASKET.DIRTY CLOGGED FUEL INJECTORS WILL CAUSE ROUGH IDLING.

rough idling can be caused by dirty air filter.dirty throttle valve and bore.vacuum leak at egr valve and pvc valve.also idling too low.will cause rough idling.

check you throttle position sensor first then fuel pressure regulator, then fuel pump. i have a 92 and had to recently do a massive overhaul. my rough idle was caused by a malfunctioning tps with a small exaust leak causing it to race and an intake manifold gasket. also check your idle speed adjustment settings.