One thing I forgot to mention: It seems to stay at fast idle (~1000-1500) when warmed up now.
I drove the car again today and it’s actually a bit hard to replicate the rapid oscillation you can see in the video. I could only get it to happen when parking after a 15 minute drive and it only appeared when I turned the AC off. When I got back to my car an hour later it was gone and didn’t reappear, even after a much longer drive home.