will idle up and down only when starting the vehicle?

Hello,

It sounds like an issue with the throttle actuator.
The vehicle is designed to have higher idle for a split second to ensure proper startup. But it goes down right away after a successful start.
If the throttle actuator is faulty it can keep the idle at a higher speed for longer and can make the idle higher.

Many times with an issue with the actuator the check engine light gets triggered.
Is your check engine light illuminated?

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

If there is trouble codes it can help with the diagnostics.

I have attached diagrams for your reference.

Please let me know of any questions.
Thank you.