See post #4 of this thread, courtesy of LastCall, thanks: Difference-between-Direct-and-Learned-Idle-Airflow

Quote Originally Posted by LastCall View Post
So I think I figured most of this out, see below:

B4515 - Direct Airflow IS Proportional idle - makes direct airflow adjustment based on error over B4509.
B4514 - Learned Airflow IS Integral idle - updates learned airflow based on error over B4508. This value is added to desired airflow based on conditions.
B4512 - Filtered RPM Airflow Correction IS Derivative. Looks at rate of change as errors approaches 0.

If anyone has anything to add in, feel free.