Surging idle

[dwarf8]

Hi all.
1989 4Runner, 22re automatic.
The idle is surging as it transitions from cold to hot. It idles fine at start-up then it surges up and down repeatedly.
Once it is hot, not more problem.
I had heard that if the coolant temperature sender is not immersed then this could be the result.
My reservoir is full and there don't seem to be any bubbles in the system.
Does anyone have any ideas I can try?

 

[Schmutz]

I realize this is going back half a century, but did you ever figure it out? Im not finding many of these threads that end with successful solutions, just cliff hangers