Power problem

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

My car idles low almost stalls (200 to 300) and when it loses power bI changed fuel filter problem still there when it shifts to 4th I lose power.

Good morning,

The first thing I would do is check the fuel pressure. You can rent one at a parts store.

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

Is the check engine light on? If it is, do you have the codes?

https://www.2carpros.com/articles/engine-has-low-power-output

https://www.2carpros.com/articles/stall-at-idle

Roy