Desired Idle Airflow

[ferocity02]

Quick question here about desired idle airflow. Why is this parameter available for the user to modify? It seems like the engine should take in whatever air it needs to maintain the desired idle speed, and then adjust fuel to maintain stoich. Seems like idle is "overdefined".

Lets say the engine needs 8 g/s at idle. What happens if the desired airflow table says like 5 g/s, or 12 g/s?

I tried doing RAFIG but the resulting desired airflow values were greater than what the MAF says. So instead I just copied the MAF vs ECT data into the desired airflow table.

Thanks!

[ferocity02]

As a followup question... Is the purpose of dialing in the idle desired airflow table to get it pretty close to correct, and then relying on the idle trims to get it exact?

I noticed the idle trims can max out if the desired airflow is way off. I also noticed some inconsistency when logging MAF flow at idle. If I let it sit and fully warm up, the hot idle MAF flow would usually be ~0.5 g/s more than if I drove for awhile and then measured the hot idle MAF flow.

[ferocity02]

Well today I learned that too high of a desired airflow will give you a hanging idle when moving. Seems like throttle cracker airflow + idle desired airflow gives the idle airflow when moving.

My idle desired airflow is turned up because I turned down my idle timing for smog. I did not adjust the throttle cracker accordingly.

[macca_779]

Desired is like the base airflow. Add cracker and yes it will hang if you have to much as trims aren't used in a non idle condition. I increase desired above what rafig generated because when reversing mine would drop low. I don't use cracker at all except in the 400rpm row as a stall saver.

[ferocity02]

Desired is like the base airflow. Add cracker and yes it will hang if you have to much as trims aren't used in a non idle condition. I increase desired above what rafig generated because when reversing mine would drop low. I don't use cracker at all except in the 400rpm row as a stall saver.

Good info. I knocked 75% off the throttle cracker airflow and it is much improved. I have tried turning cracker off, but it would surge and try to die when rolling in neutral. I'm confused as to what's different between rolling idle and stationary idle. Are you suggesting it's not actually in idle mode when rolling in neutral with the throttle closed?

[macca_779]

Good info. I knocked 75% off the throttle cracker airflow and it is much improved. I have tried turning cracker off, but it would surge and try to die when rolling in neutral. I'm confused as to what's different between rolling idle and stationary idle. Are you suggesting it's not actually in idle mode when rolling in neutral with the throttle closed?

No because you have the speed enabler in preferences which allows idle mode to kick in

[ferocity02]

What would happen if I set the speed enable such that it was always in idle mode when the throttle is closed, rolling or not, and then disabled throttle cracker?