High idle issue

Also, as I said, the rear 02 sensor was reading rich because it was nearly matching the front o2 sensor voltages. So, not lean but rich, which is what's throwing me for a loop. But maybe I'm thinking it wrong and getting confused.

I didn't have access to a leak down tool but did a similar test. Compression was 125 on cylinder 1 compared to 160-175 on the others. I used an air compressor and the hose from my tester and aired up cylinder 1 at TDC, all valves were leaking and held zero pressure. One time out of ten I got enough pressure to build to leak out and close the intake valves but exhaust side was still leaking. Lol. So sticking valves. I left a half a can of seafoam in there overnight and retested. Better compression at 150, but valves are still sticking partially open. I did an "italian tune-up" and ran it at high rpm after and successfully burned up some of the buildup as my idle improved but it's still elevated and unsteady. So, she needs a valve job.