these statements apply to any ecm not yours specifically

the iac doesn't have anything directly to do with idle mixture. it uses it to control idle speed instead of moving the throttle plate like a carb or fly by wire engine. the computer meters its fuel to adjust the AFR, it doesn't add airflow to meter its AFR via the IAC. in other words the IAC adds airflow and the computer takes that airflow and calculates the fuel

your idle 'speed' is controlled with most modern ecms by a combination of IAC and timing advance

your idle 'mixture' is controlled by a combination of your VE table (or maf table if maf equipped) and the startup enrichment tables or whatever that takes the coolant temp and/or intake air temp and/or a 'time since start' timer and adds enrichment fuel, this is what replaces the 'choke' in a carb