E38 idle airflow

[KenB]

Where is the idle airflow or throttle angle set? I see the over/underspeed corrections but where is the airflow value set?

Have a car here with a cam and it will idle ok, but if you rev it in park, it drops way past idle and will recover at about 400 RPM. Any help would be appreciated.

Ken

[swingtan]

Try B1829....

[hymey]

Set you idle airflow at about 9.5 to 10.0 at around 800rpm to start with. experiment up and down. I find the best setting is about 1g/s below what is measured through the MAF at idle, it wont hang yet wont drop or hunt. Watch what your average timing is at idle and set it at the average, take further logs. You will find it is sensitive to idle timing values. While some people run well over 20 degrees idle timing I have had success with less than 20, Seams to help the engine idle lower without hunting. Also depends on cam overlap.

Joel

[KenB]

Set you idle airflow at about 9.5 to 10.0 at around 800rpm to start with. experiment up and down. I find the best setting is about 1g/s below what is measured through the MAF at idle, it wont hang yet wont drop or hunt. Watch what your average timing is at idle and set it at the average, take further logs. You will find it is sensitive to idle timing values. While some people run well over 20 degrees idle timing I have had success with less than 20, Seams to help the engine idle lower without hunting. Also depends on cam overlap.

Joel


Set it where? 1829 which was posted is minimum idle airflow. Is this the proper place? This is on an auto 08 vette. I did play with that table and didn't see any change when adjusting this table. The highest I've gone is 9.5 so maybe it just needs more.

Car will start and idle. Startup is a bit rough, but once it idles it's fine. Fuel trims are very good. But if you rev it, on the way back down it goes past the idle setting all the way down to 400 and then usually recovers. The higher you rev it, the lower it overshoots idle. The recovery comes with more throttle angle.


Thanks for the replies

Ken

[swingtan]

Once you have adjusted the Min idle air flow, low the idles and watch what happens when you give it a rev in neutral. You may find that the spark advance is dropping a bit far as it comes back to idle and causing the idle speed to drop too far. It may help if you post up a log file and the tune file.

Simon

[KenB]

I got it worked out. The label minimum was throwing me off. I would think it would be commanded idle airflow. I figured min was a low clip and you didn't want to use that one. Plus when I raised it, it did't seem to help. problem was I didn't raise it enough.

thanks,

Ken

[Mike@sic]

Once you have adjusted the Min idle air flow, low the idles and watch what happens when you give it a rev in neutral. You may find that the spark advance is dropping a bit far as it comes back to idle and causing the idle speed to drop too far. It may help if you post up a log file and the tune file.

Simon

what is the best way to cure this issue, dropping to far and then correcting itself / surging until it comes back to idle.

[Taz]

Hello Mike,

The E38 Idle Tuning sticky (by Hymey, Swingtan, and many others) has pretty much all the information you need to tune a solid idle with a modified Gen IV controlled by an E38 / E67.

Link is below ...

http://forum.efilive.com/showthread.php?9740-E38-idle-tuning

A very general overview of the information in the sticky ...

disable B1844 & B1845 (Integral Step / Proportional Step)
disable B1829 (Minimum Idle Airflow)
then setup B1652 (Idle Area 2 - stationary) until the idle spark advance is where you want it
then enable B1844 & B1845 (try reducing each by 50%)
then enable B1829 - adjust until you have a stable idle (too low - idle will drop too much, too high - idle will take awhile to settle)
then adjust idle spark advance to arrive at the idle quality you wish (choppy vs smooth)
Regards,
Taz

[Mike@sic]

thanks man, yea ive been reading that thread trying different things. ill give it a go, im just trying to work some small issues out now.

[swingtan]

As usual, logs of the issue are the easiest way to help out. There are many different calibrations that impact how the engine come back ti idle and the surging can be set off by many things. A quick method of removing some surge is to bump up the min idle airflow, but it's not the only fix. I get no surge and have my idle airflow set to 7.6gm/S, it's all in the fine tuning. But it's hard to give an answer without actually seeing the issue in the logs, as there's probably a number of parameters that need adjusting.

Simon

[ringram]

Upping the proportional and integral correction values can help too. its definitely an art rather than a science.
Though in theory it should be pure science!

[Naf]

Try raisin the airflow correction 1602, i had a decent idle, but only when stoppin it dropped down then surged up. I raised mine from .25 to .325 at 90 and 104c and it feels good. If you feel the car creepin forward too much while you are pressin the brakes, then lessin it slightly.

My idle use to drop to 300rpm then jump to 1500. Try doin that in traffic with 2000$ spot lights on the front of your truck...