In closed loop operation the mixture is maintained at stoichimetric except at WOT. The idle speed is controlled by the ECU and is not adjustable, other than the basic adjustment to keep the idle control valve duty cycle in the proper range.

The basic mixture adjustment is okay if the car starts and runs well when cold and the duty cycle is in the correct range, which appears to be the case with your car.

It's not broken. Don't fix it!

Duke