Generally, a result of lean idle conditions. Try increasing the lower RPM VEs by 10-15 points on either the front or rear VE tables.

Program these changes to the ECU and see if the condition has improved. Some stock exhausts do not provide the rear oxygen sensor with good exhaust sampling and this prevents any automatic adjustments or indicators that would show or fix a problem. Having one cylinder too lean often leads to the engine sounding like it is running on one cylinder (like a tractor) at idle.