Hello,
It sounds like you might have a faulty Idle air control valve (IAC).
The IAC control the idle and a faulty IAC can cause the idle to be unusually high.
Many times cleaning out the valve will fix the high idle issue. Simply take the IAC off of the throttle body and clean it out with good quality parts cleaner. Wait for everything to dry and reinstall.
Here are some helpful article on how to service the IAC:
https://www.2carpros.com/articles/how-a-idle-air-control-valve-works
https://www.2carpros.com/articles/idle-air-control-valve-service
https://www.2carpros.com/articles/engine-idles-too-high
For the P0404, typically you will get that code if the EGR valve is clogged.
You can also clean out the EGR as well.
https://youtu.be/DqUCbbKdWf4
I have also attached the diagrams for the IAC and EGR
Please let me know of any questions.
Thank you.
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Wednesday, August 4th, 2021 AT 9:58 PM