Engine revs up and down

The fact that the vehicle shifts to neutral is odd. Does it actually pop out of gear or does it just act like it is in neutral? The fact that this is a manual transmission makes this really strange as that is a completely "manual" system. Meaning you control it and the control modules cannot physically change the gears.

So I suspect it just feels like it is in neutral or it is just popping out. This high idle issue sounds like a vacuum leak so let's start there. Here are some guides that will help with this:

https://www.2carpros.com/articles/engine-idles-too-high

https://youtu.be/4ktw1X4W_-k

Please run through this material and let us know what you find and we can go from there. Thanks