Idling problem

This sounds like it is a possible vacuum leak, so we need to start with this.

Here is a guide that will get us started:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Basically, what is happening is there is a leak in the air intake/manifold after the sensors, so the PCM doesn't know this air is coming in. So, as it reads the o2 sensor data it is constantly trying to adjust for this unknown amount of air.

Here is another guide that will help with explaining the possible causes:

https://www.2carpros.com/articles/engine-surges

However, let's use brake cleaner around the manifold and see if the RPM smooth out or raise slightly and that will prove out a vacuum leak.

Once we know where this is we can figure out next steps but if there is no vacuum leak then we are going to have to monitor the mass air flow sensor data. You may even want to try and clean it so here is a guide that will get us down that path:

https://www.2carpros.com/articles/mass-air-flow-service

Thanks