Have you ever checked the idle air control valve (IAC)? The IAC is what is responsible for maintaining engine idle speed. Since the idle speed changes, I would remove and inspect it for carbon as well as in the intake manifold. If there is an air obstruction, it will cause issues.
If you look at pic 1, it shows the IAC. Here is a link that explains how to service one.
https://www.2carpros.com/articles/idle-air-control-valve-service
Let me know.
Joe
Image (Click to make bigger)
Friday, February 11th, 2022 AT 7:33 PM