Looking for some help/advice on E38 Idle

[smokeshow]

Perfect world... But you can't account for every scenario. Not trying to trick you lol...they exist for a reason.

[edcmat-l1]

Perfect world... But you can't account for every scenario. Not trying to trick you lol...they exist for a reason.

I agree. I don't think you're trying to trick me or anyone. I look at the PIDs as blade control and that's it. I don't use them to aid in idle recovery, return to idle (dashpot) any other situation other than blade control.

[Alvin]

The issue I and I think a few others are trying to express is..

usually fueling / bad idle timing setup is the cause of idle issue. But instead of taking the time to get those dialed in people jump into the PID side of the throttle control. Base Airflow has to be dialed in. But beyond that most of these guys are digging themselves in a hole patching a bad idle due to bad airflow models with PID tuning.

PID tuning is not exactly straight forward either. People are just guessing. Most people don't even know what diff eq or laplace transforms are.. Even if they do.. Most people aren't at that level in math. This was after calculus 3 for me.

Quite often idle issues are because the engine transients though a rich region of the VE table you don't see often in steady state operation, just in engine decel. Or they are trying to use a MAF with a huge cam, or they are trying to use narrowbands to tune fueling with a cam with a ton of overlap.

my advice is to iron out the basics before even thinking about touching the pid side of idle control.

[mbray01]

the issue i and i think a few others are trying to express is..

Usually fueling / bad idle timing setup is the cause of idle issue. But instead of taking the time to get those dialed in people jump into the pid side of the throttle control. Base airflow has to be dialed in. But beyond that most of these guys are digging themselves in a hole patching a bad idle due to bad airflow models with pid tuning.

Pid tuning is not exactly straight forward either. People are just guessing. Most people don't even know what diff eq or laplace transforms are.. Even if they do.. Most people aren't at that level in math. This was after calculus 3 for me.

Quite often idle issues are because the engine transients though a rich region of the ve table you don't see often in steady state operation, just in engine decel. Or they are trying to use a maf with a huge cam, or they are trying to use narrowbands to tune fueling with a cam with a ton of overlap.

My advice is to iron out the basics before even thinking about touching the pid side of idle control.

bingo

tuning is a case of less is more

the less you do to get the vehicle happy, the better everything will be. Get the basics right, and most of the advanced stuff is never needed

[edcmat-l1]

The issue I and I think a few others are trying to express is..

usually fueling / bad idle timing setup is the cause of idle issue. But instead of taking the time to get those dialed in people jump into the PID side of the throttle control. Base Airflow has to be dialed in. But beyond that most of these guys are digging themselves in a hole patching a bad idle due to bad airflow models with PID tuning.

PID tuning is not exactly straight forward either. People are just guessing. Most people don't even know what diff eq or laplace transforms are.. Even if they do.. Most people aren't at that level in math. This was after calculus 3 for me.

Quite often idle issues are because the engine transients though a rich region of the VE table you don't see often in steady state operation, just in engine decel. Or they are trying to use a MAF with a huge cam, or they are trying to use narrowbands to tune fueling with a cam with a ton of overlap.

my advice is to iron out the basics before even thinking about touching the pid side of idle control.

Yes, same thing I've been trying to say for 3 pages just with less words.

I've been trying to focus on (for the sake of the thread) idle stability. NOT return to idle, idle transitions etc., because I think that's what the OP started the thread about. And ESPECIALLY in this scenario, AT REST IDLE STABILITY, PID controls are the LAST thing you want to be modifying.

[smokeshow]

Lol I assumed that went without saying, especially given that the VE was likely the root cause of the problem....base cal must be complete before idle, driveability, etc. That's definitely not under contention... Doesn't make me agree with a blanket statement to completely disregard certain idle controls though.

[ns158sl]

How do you guys go about picking a timing value for idle? I use to use vacuum but then that kind of throws out torque reserve. Ive always just went with "feel" and that seems fine so far. I guess if a guy has a dyno at his disposal, what would be a general rule of thumb for a torque reserve, if even possible on measuring on a chassis vs an engine dyno?

[Cringer]

How do you guys go about picking a timing value for idle? I use to use vacuum but then that kind of throws out torque reserve. Ive always just went with "feel" and that seems fine so far. I guess if a guy has a dyno at his disposal, what would be a general rule of thumb for a torque reserve, if even possible on measuring on a chassis vs an engine dyno?

Idle by vacuum is for carbs. Use a lower value for base idle like 12-15*

[ns158sl]

Yep. That's why I was curious if other people are doing what I do by 'feel' or an actual hard number or what the factory was using.

[TragicMike]

Extreme newbie question here, but this is already a helpful thread and it seems like a proper place to ask:

What factors control idle fueling on the E38?

Is it strictly Airflow Final Minimum and VVE, or is MAF Airflow in there as well?

[hjtrbo]

MAF and VVE. There is bias towards one over the other but that is a whole nother topic

fishing-8454_256.gif

[Alvin]

I normally setup Gen 4's around 18 degrees for idle.

Leaves plenty to go in both directions to save/lower idle.

[edcmat-l1]

Agreed. 18 degrees seems to be the sweet spot for a lumpy cam.

[hjtrbo]

18 is my number also

[smokeshow]

18 is a little young...but if that's what you like, then get after it.

[sgod1100]

18 is a little young...but if that's what you like, then get after it.

I mean, LEGALLY, it isn't...lol

[hjtrbo]

What we say here in Oz and to really drag down this thread; if there's grass on the wicket...

[Allen Vos]

I wish there was more of a half ass explanation on how to tackle Prop vs Integral for idle swings. I know people say stock are fine. Well there are quite a difference between say a 5.3 and an ls7 lol. So far softening Prop as little bit seemed to help, but then I added integral to quicken up the idle oscillation. Seems better overall but it still has a surging. I will be curious what the OP will post once his VE is dialed in.

OK guys, so I finally was able to spend a bit of time with the car.

I flashed the car tonight and the only changes are the Modified VVE table from Ed, and I got the startup air flow dialed in a bit better.

I did not change the Idle integral or proportional Table or the spark over and under speed tables as I did not want to make to many changes at once

It fired up and had a small amount of surging on cold startup for only a few seconds but then the idle pleasantly settled and came down to 800 rpm once it warmed up a bit and idled very steady with no surge at all.

I have included a Log and the Tune file.

I noticed the VVE g/s numbers were not perfect but a hell of a lot better than what they were.

To be honest I'm quite happy with how this thing starts up and idles now. I'm sure there is a bit more tweaking needed. I feel I can drop the startup airflow down a little bit more and possible the min air flow a half a gram or so.

Have a look guys and let me know what you think.

I'm not even sure I should touch the inegral or proportinal tables or the spark over and underspeed tables? What do you guys think?

I may mess with them and throw them all back to stock as Ed has reccomended on the weekend just to see if it makes any difference.

As far as the integral and proportional tables go I've read I should be using either a 2010 CTSV, a 2014 Camaro or a 2013 Vette A6 as opposed to my 09 vette stock ones

Any idea which would be more suited for my setup? Keep in mind its a manual car.

The other thing I have been reading is that the torque follower table needs to be set up.

I logged engine torque but at idle its only coming up at 20-30 NM which is roughly 15-22 ft lbs of torque.

Does this seem accurate?

From what I understand the torque value needs to be put into the torque follower table at the appropriate idle speed?



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[Allen Vos]

Extreme newbie question here, but this is already a helpful thread and it seems like a proper place to ask:

What factors control idle fueling on the E38?

Is it strictly Airflow Final Minimum and VVE, or is MAF Airflow in there as well?

I am recently new to this as well, and from what I understand Dynamic air flow is what the ECM uses to calculate fueling. Dynamic Air Flow is a calculation from both VVE and MAF.

Air Flow Minimum is your minimum air flow at idle and helps control your idle speed and recovery.

If I am wrong, I'm sure someone will correct me.

[ns158sl]

I'd leave the idle airflow tables stock. Ive tried data from other cals and it just didn't seem to work that well. Especially without knowing exactly how the tables affect airflow and spark, better off to tweak what you have (if even needed) and then you know how it is helping your idle. Throttle follower is magic, lol. I'd probably add around 10 15 ft lbs from 1200 or 1400 and down, again a 5.3 cal has negative torque in throttle follower whereas an ls7 has 80 ftlbs. . You can add more if needed later if you see how it is helping off idle transitions. Smokeshow has talked about how this table is important for cam changes. I can't find the thread right at the moment.