I'm still in the early stages of tuning because it's my first time and I'm learning still but I've noticed this.

When in open loop my car idles like a champ the way I got it setup. Driving, coming to a stop etc. All good.
Closed loop is hit or miss. It idles "ok" sometimes. Most the time the car sounds like it's missing when idling and often it will surge real bad and die, have to keep re-starting and use the gas pedal to feather it. Put it back in open loop and it idles like a champ.

Do long and short term fuel trims in normal cruise and driving affect idle? could that be why?

 

What software and hardware are you using for tuning?

Some software has open loop and closed loop fuel corrections that can be adjusted.

 

Ah sorry, S300.

 

Open SManager, load your calibration, select Parameters, select the Closed Loop tab and configure your closed loop options. There are also closed loop compensation options in the Fuel compensation tab. You could also look under the idle tab and see if making adjustments to your idle speed vs coolant temperature (moving) table would help.

In the closed loop configuration you can set the short term fuel trim settings.