Based on your description, it sounds like the idle air control valve is failing. Anytime a load is placed on the engine, this valve allows additional air to enter the engine to adjust for the load. If the RPM's are jumping up and down, chances are it is failing. Here is a quick test. See if it does it in neutral or park with the AC on. If so, this is the issue.
Now, I attached two pics below to help you locate the component. Locate it and inspect wiring to it first. Next, remove it and inspect it for dirt or damage. Here are a couple general links you may find helpful:
I don't know how handy you are, but here are the directions for checking the part in question. The remaining pics include the directions.
Here are a few links you may find helpful when testing:
Let me know if this helps. Also, feel free to let me know if you need help or have other questions.
Images (Click to enlarge)
Tuesday, January 28th, 2020 AT 7:15 PM