For months now I've had a rough idle in the 4L engine. Idles smoothly when first started, but within 2-3 minutes the idle sounds like a spark plug misfiring. Runs smoothly above idle. Turn it off, let it sit only a minute or two, (even if hot) start it back up and it runs smoothly again for a couple of minutes. On rare occasions, it will for no apparent reason decide to idle smoothly all on its on!

Have: new injectors, new fuel pump, new pressure regulator (none of which was installed to address this problem) new oxygen sensor. It is not a cylinder misfire. Pulling any single plug wire will roughen the engine, indicating all plugs are firing. My suspicion is it is a sensor that, when it warms up, it shortens the injector pulse width.

Any thoughts?

Check AutoZone Web. They have a idle speed sensor and show your where it locate.

thats what i would do