Taurus idling rough

2003 Ford Taurus, 3.0l V-6, auto. Started idling rough 3 days ago. Seems to run fine at speed and acceleration not affected. Usually idles smoothly for several minutes after starting or after coming to a stop. Then the rpm drops about 100rpm and begins “chugging” or surging. The tach swings up and down several hundred rpm. Hit the gas and it revs up smoothly but once it settles back down to about 900rpm it gets rough again. Plugs and wires replaced 3 months ago. Coil swapped out early last year. What could cause this?

It is surprising how many people have posted problems due to regular maintenance items such as air and gas filter, possibility?

The problem might be with a dirty/defective Idle Air Control valve. This component is what controls the engine idle speed. And because the engine smooths out as soon as the accelerator is depressed, or taken off of idle, that would be the first thing to check.