Vibration while stopped and fluctuating RPM's

This could be the result of many things such as needing a tune up, a problem with the idle air control valve, fuel pressure issues, a vacuum leak, and so on. Is the check engine light staying on when the engine is running? If it is, you need to first scan the computer for trouble codes. Here is a quick video showing how that is done:

https://youtu.be/YV3TRZwer8k

I realize most people don't own a scanner, but most parts stores will do it free of charge for you or rent / lend a scanner to you.

Now, here are a few links to help check some of the things I mentioned:

https://www.2carpros.com/articles/how-to-tune-up-a-car-engine

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

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Please keep in mind, with the number of miles the vehicle has, engine compression and timing can play a role with this problem.

Let me know what you find.

Joe