The most common cause of this is a vacuum leak. Here is a guide that will help with this:
Also, here is a guide that will help with surging issues:
Basically we need to run through this and determine what the cause is. Clearly it could be a couple things but the most common are intake manifold leaks or hose leaks.
So here is a video that will help as well. It covers the same basic info but some people just prefer videos.
Let us know if you have other questions. Thanks
Friday, December 4th, 2020 AT 2:12 PM