1992 1.6 8V with TBI.  Rebuild with new head, good compression, all fresh ignition parts, virtually new motor and it purrs like a kitten, has great power and starts easy, BUT...

Once it warms up to about 180, the idle starts to surge and begins to start this rhythmic high low alternating idle dance that drives me nuts.  This condition just started about 2-3 days ago and has never given me issues before. 

Been reading about vacuum leaks, none that I can find.
I did the hose trick to block the internal wax pellet vacuum port but still no luck.

Once again, the motor still performs great and drives like it should but at a stop light it sounds like I'm revving my mighty 90hp and tempting the vette next to me to a race.  NOT what I had planned!

Any help?  From everything I've read there are lots of directions this can go?

Drove around a bit at lunch today trying to pinpoint when it starts and what effects the surging idle.

Started it and let it warm up in the parking lot, idle was fine, temp is about 78 degrees outside today, nice and sunny.  Once it warmed up to temp it idled fine.  I have a real temp gauge so I know it was running right around 180, temp came up just over 180, the thermostat opened and you can see the temp drop back down.

I got in, depressed the clutch and the idle started immediately pulsing.  Let off the clutch, still out of gear, and it leveled out again?  While sitting in the parking lot I could control when the pulse started and stopped with the clutch. 

Drove around a bit and I was still able to control the surge at stop lights by just putting it in neutral and not holding the clutch in.  Idle fine.  After a couple stops it didn't seem to matter what i did, the idle pulsed high/low.

What the heck could a cable clutch depression have to do with causing a difference in idle?

This sounds to me like among the odd things that happen when grounds get iffy. Try pulling & cleaning as many ground points as you can find & see if it helps. What might be happening is [whatever idle control is failing] is (wrongly) using the clutch cable for a ground, & when you disengage the clutch it loses the ground.