You may have two issues. Low idle sounds like an IAC issue because this is what controls the idle speed. To lose power in 4th gear only does not sounds like a fuel issue or air control issue. It normally doesn't effect one gear like this.
Run through the test that I provide for the IAC. Then take a look at the video and check the basics for the loss of power. Hopefully if we resolve the idle issue it will fix the other but I would start there.
https://youtu.be/U1RoG3I-Oww
Images (Click to make bigger)
SPONSORED LINKS
Wednesday, December 11th, 2019 AT 4:08 PM