Commanded Idle Base Running Airflow vs Actual >

[Turbo6TA]

2011 Corvette LS3 with Heartbeat PD supercharger (E38 ECM)

Cam: .220* / 234* . ..585"/.585" . .118* LSA

775 Idle RPM

18* Idle Timing (This is also the commanded idle timing)

-16 in/Hg Idle Vacuum

14.9 Idle AFR​

+4% Idle LTFT

MAF only tune
___________________________

As you can see by the chart below, I have my Idle Base Running Airflow set to .10.00 g/s .(1.32 lb/min)

However, when idling at normal operating temp, the HP Tuners scan reads approx .11.40 g/s .(1.51 lb/min)
___________________________

Can anyone tell me why the actual idle airflow is higher than the commanded idle airflow? . The engine idles nice and smooth and the car has no drivability problems at all. Throttle response is excellent.

Am I worried about something I should not be concerned about?

Thanks,
Ron

[Mr.z0611]

A data log with correct channel list will show exactly what's going on. 10 g/s + 4% error = 10.4
Also, it seems like adaptive idle is adding more air to target your rpm goal which is 775 to minimize % error between commanded and actual rpm. Nothing to worry about.

[Turbo6TA]

Mr.z0611

Thanks for the response ... I was thinking that maybe I should increase the Final Idle Airflow numbers from 10.00 g/s to maybe 11.00 in order to get it better inlined with the actual 11.40 g/s that I am seeing while doing an idle rpm scan.

But, like you said ... "Nothing to worry about"

[Mr.z0611]

You can test it out. Save the tune to go back when you need it. I would add 0.6 g/s to BRAF and 4% to maf curve in idle freq.

[Turbo6TA]

. .

[pannetron]

The disparity could be because the MAF isn't calibrated well or very accurate at low air flow.

[07GTS]

yea u want the idle trims to control the idle above and below and no just sit on the floor so to speak, so a little space below commanded is fine u only want to catch it if it goes too far with the limits, look at the dynamic airflow that is the reading that is used by ecu

[Alvin]

2011 Corvette LS3 with Heartbeat PD supercharger (E38 ECM)

Cam: .220* / 234* . ..585"/.585" . .118* LSA

775 Idle RPM

18* Idle Timing (This is also the commanded idle timing)

-16 in/Hg Idle Vacuum

14.9 Idle AFR​

+4% Idle LTFT

MAF only tune
___________________________

As you can see by the chart below, I have my Idle Base Running Airflow set to .10.00 g/s .(1.32 lb/min)

However, when idling at normal operating temp, the HP Tuners scan reads approx .11.40 g/s .(1.51 lb/min)
___________________________

Can anyone tell me why the actual idle airflow is higher than the commanded idle airflow? . The engine idles nice and smooth and the car has no drivability problems at all. Throttle response is excellent.

Am I worried about something I should not be concerned about?

Thanks,
Ron

There is a lot of confusion in this thread.


The final Idle airflow minimum is like the low limit of where the throttle body blade position will go to.. Or its base to start with before all the other adders. This doesn't correspond to how much air is actually going into the engine. This sets idle airflow only. Nothing for fueling.

I noticed someone mentioned idle trims... LTFT is fuel trims. This isn't a idle airflow trim. This is a fuel trim. Anything later than GEN 3 we cannot scan idle airflow trims. You can generally tell if the idle airflow table is too high or too low by the amount of timing the engine is using to hold the idle. Too high timing and the final idle airflow minimum table is too low... too low timing and the final idle airflow minimum table is too high.

[Cringer]

Anything later than GEN 3 we cannot scan idle airflow trims. You can generally tell if the idle airflow table is too high or too low by the amount of timing the engine is using to hold the idle. Too high timing and the final idle airflow minimum table is too low... too low timing and the final idle airflow minimum table is too high.

I would disagree somewhat. It is not a simple trim, as this is controlled with a PI controller. And thus you can log both the [Idle Proportional Airflow] and [Idle Integral Airflow] PIDs in the scanner. When your airflow and spark is spot on these should be dancing on zero.

[Alvin]

I would disagree somewhat. It is not a simple trim, as this is controlled with a PI controller. And thus you can log both the [Idle Proportional Airflow] and [Idle Integral Airflow] PIDs in the scanner. When your airflow and spark is spot on these should be dancing on zero.

It might be new.. I'll be excited to look for it.. What pid number specifically are you looking at?

[Cringer]

It might be new.. I'll be excited to look for it.. What pid number specifically are you looking at?

Pretty sure they have been there the whole time. Not sure of the numbers, but they are under engine > idle in the scanner.

[Alvin]

That's cool. I felt like I re-looked for something like this just a couple years ago and didn't find it.


Things are always evolving. For the longest time we had just shift schedules and master TM for 6l80e's.. Dumb things like injector offset vs tip temp come later etc.

[07GTS]

early e38 didn't get the idle trims but the later did, some of us still have to guess based on spark and commanded idle rpm v actual rpm