When the idle is fluctuating, you can actually watch the throttle mechanism bounce back and forth. Something is telling that solenoid to move in and out, just not sure what.

This weekend I checked the grounds, and the body one was a bit gritty. Wire wheeled and reassembled with some dielectric grease. The resistance from the throttle body to the negative post on the battery is very low, so that connection would seem to be good. The problem still seems to be there, but I noticed some of the jacketing on the throttle position sensor wiring is cracking. I'm going to hit it with a bit of liquid electrical tape and try to make sure everything is sealed up as best it can be there. The truck is also showing a bit of a miss now at idle, not sure if it's related or not. It got a fresh distributor cap and rotor during maintenance not long ago, might try pulling the plugs and see if there's a smoking gun there.

Gotta get ol' Frank in top shape soon!