My '95 PS F-350 4X4 service truck has always had a rough/lopey idle (since I've owned it). I hardly ever drive it so I've kind of ignored it.
Tonight I unplugged the ICP and it did seem to smooth out, not totally but at least 50% better anyway.
I unplugged it a few times just to convince myself it really was making a difference.
I also had an ABS light on so I decided to disconnect the negatives on the batteries while I went in and looked for a deal on a new ICP. (Found one for $80)
NOW the engine dies if you unplug the ICP.
Is this because the "computer" has "reset" and it hasn't "remembered" the default settings?
That's the only thing I can think of.

 

If you find oil in the plug, your icp is shot or going out.

I would think you are correct. The truck hasn't had time to learn, and the sensor is feeding it bad data.