What does base running airflow physically control

[thebeewantsboost]

I was trying to understand the theory of it, is it an air table, consequently adding fuel. Or does it control the iac valve? Or something else

[wildkard]

It really is exactly what it says, it's the average amount of air the engine requires to maintain idle rpm. The computer uses it as a starting point for adaptive idle, which will vary spark advance and throttle blade/ iac motor position to adjust from that position.

[mowton]

Actually the Base Running Air or RAF is the minimum amount of air the PCM will start from and as wildcard stated, all other adaptive idle corrections, Fan Airflow, AC Airflow, Throttle Follower/Cracker etc. will be added to it to develop what is called Idle Desired Airflow. In both the DBC and DBW configurations, this Airflow is converted to a millimeters squared opening value representing an opening size matching the air requirement. Then, based on whether the the idle air is managed by an IAC (DBC) or Throttle Blade (DBW) and throttle body size the PCM converts the opening size into IAC steps (effective area vs IAC Steps) or commanded TPS% respectively.

That is why when tuning idle, it is important to make sure non of the airflow adders are active during the establishment of the BRAF settings. We disable the fans, shut off the AC, don't touch the pedal etc to make sure only the RAF is being used to establish the idle. The only two elements we want during this effort is obviously the RAF and Adaptive Idle corrections (LTIT and STIT). That is why we log Idle Desired Airflow and copy ir into the RAF table to lower the Adaptive idle correction to zero to establish our final RAF value.

Ed M

[anniversaryss]

Actually the Base Running Air or RAF is the minimum amount of air the PCM will start from and as wildcard stated, all other adaptive idle corrections, Fan Airflow, AC Airflow, Throttle Follower/Cracker etc. will be added to it to develop what is called Idle Desired Airflow. In both the DBC and DBW configurations, this Airflow is converted to a millimeters squared opening value representing an opening size matching the air requirement. Then, based on whether the the idle air is managed by an IAC (DBC) or Throttle Blade (DBW) and throttle body size the PCM converts the opening size into IAC steps (effective area vs IAC Steps) or commanded TPS% respectively.

That is why when tuning idle, it is important to make sure non of the airflow adders are active during the establishment of the BRAF settings. We disable the fans, shut off the AC, don't touch the pedal etc to make sure only the RAF is being used to establish the idle. The only two elements we want during this effort is obviously the RAF and Adaptive Idle corrections (LTIT and STIT). That is why we log Idle Desired Airflow and copy ir into the RAF table to lower the Adaptive idle correction to zero to establish our final RAF value.

Ed M

So basically the pcm starts with BRAF then adds or subtracts won't the adaptive measures.

[mowton]

So basically the pcm starts with BRAF then adds or subtracts won't the adaptive measures.

I think won't should be what,,,correct. All the additional airflow factors are added/subtracted to it as I stated above. The adaptive idle LT and STIT are just a part of it but when tuning the idle you only want thos two parts because you want to offload all the error back into the RAF table. There is a better list in the Tutorial which defines each but you can go through the Idle tables and find them. Startup abd Friction Air are two more. The RAF defines the lowest the Idle Desired airflow can go...

Ed M

[anniversaryss]

I think won't should be what,,,correct. All the additional airflow factors are added/subtracted to it as I stated above. The adaptive idle LT and STIT are just a part of it but when tuning the idle you only want thos two parts because you want to offload all the error back into the RAF table. There is a better list in the Tutorial which defines each but you can go through the Idle tables and find them. Startup abd Friction Air are two more. The RAF defines the lowest the Idle Desired airflow can go...

Ed M

Yes I sorry Ed my phone autocorrect gets me all the time.

What I meant was BRAF is the starting airflow whereas after that the adaptives correct it.

I just got through your adaptive section..... moving on.