Idle surging once car comes to complete stop...

[DSteck]

The positive numbers in your overspeed table have probably been screwing you over.

[Snyper]

Im going to go check that out right now.

[DSteck]

Im going to go check that out right now.

I did that once by accident... ran positive numbers in an overspeed table. I was wondering why the idle wouldn't stop flaring and surging really hard.

[extents]

Looking at your latest posted tune, you cannot run zero airflow 1600 rpm and above. This is why your tach needle will drop like a rock when you push the clutch in and then ramp back up. You must have some airflow still during coast down while coming to a stop.

Your coast down spark table looks good, but you're still pulling too much timing in your coast down overspeed table. This can make things bounce around a bit as well. You could probably max 8.5 degrees being pulled, just like what you're adding on underspeed.

[Snyper]

Heres a current tune file. I fixed those issues before and its still happening. It seems like its only when the car comes to a complete stop. I lowered the overspeed correction and even upped the underspeed timing correction and it didnt seem to work. If im doing say 60 mph and I push the clutch in the car will go down to idle and stay there (which is set to 1200 above 3mph) as soon as the car comes to a COMPLETE stop(the very second) the idle dips to nothing and stalls..the same thing happens if im doing 60..downshift and then put it into neutral. Doesn't make any sense. Once the car catches its idle it holds it steady.

[extents]

From 64 rpm and up pull 6 degrees max in your idle overspeed. When you hit a complete stop and the tach dips I think it's because you're pulling 10 degrees off your idle spark. What's your timing say at the instant you hit zero mph? I'm guessing 7 degrees or less. Low timing = less power = stall....

Not sure why you have less timing pulled in the later rpm's on your idle overspeed and more pulled in lower rpm ranges. Just pull 6 degrees tops from 64 rpms and above. Do the same with your coast down tables.

Call me crazy but I think you're running hardly any idle airflow. I would almost double what you have currently all the way up to 1600 rpm. At least give another 75%...

[Snyper]

Im running a 50% scaled tune.

[extents]

My mistake... See that posted earlier ...

[Snyper]

I wonder if Im still running MAF too low. I used the method 5LE used to find the MAFs but they werent enough. I had to add about 30%..I wonder if I have to keep adding. I never had this problem last year and the only things different this year are CNCd heads, FAST102 and a built bottom end..the cam is the same.

[Snyper]

Ok I fixed it. Heres what I did...I doubled the enable rpms for both integral and proportional RPM error. Also, just as a "what if" I doubled my Min AFs so that they are now above what I was running last year with the non scaled tune..and it completely took care of the issue. No RPM dipping whatsoever whether im at idle, slowing down in neutral or using my transmission to slow me down. It does right to where its supposed to and stays there.

[DSteck]

I'm under the impression that final idle airflow (and startup airflow) shouldn't be scaled. I've had good luck NOT scaling those items. I think they're treated similar to idle airflow in LS1 PCMs where the airflow values are independent of what's actually happening.

[Snyper]

Yeah, that would make sense. My startup flows when halved screwed everything up as well.

[pontisteve]

X2 on confusing the + and - in the over/under tables. Easy to do, and definitely makes things worse not better!

I've had good luck not touching the PID idle stuff. Also with reducing the over/under values below 150 RPM. Above that RPM error, more drastic measures must need to be taken, and thus the larger values. But I do think the factory goes too far with that for aftermarket cams.

I look at the timing values at idle, and if they're jumping around a lot, the idle usually stinks. When they're not moving much, the idle is steady. This makes me want to not move them much by limiting the over/under.

[DSteck]

Spark ends up being pretty jumpy with huge cams for me but the idle stays steady. Maybe I'm just not doing it right but screw it, it works.

[Snyper]

Hahaha yeah mine jumps around 1-3 degrees at idle and it idles rock solid now.

[edcmat-l1]

Ok I fixed it. Heres what I did...I doubled the enable rpms for both integral and proportional RPM error.

^^^This is what I was talking about here vvvv

Also, for idle control, it's better to have the over and under speed spark tables more agressive in the lower RPMs, and lessen the RPM adaptive idle controls, which slows down the throttle blade correction, which is more responsible for idle problems than the spark tables.

[Snyper]

Cars running like a dream now. First time since ive had the turbo setup(since last year) that its ran this good.

[pontisteve]

I've been under the theory that a cammed car wants to lope a little no matter what, and if we try to force out those low RPM errors, we would just start rocking the boat until it oscillated out of control.

But come to think of it, I was basing the cam wanting to lope no matter what on the fact that straight up cammed carbureted cars with fixed timing lope, and that amount of lope could not be removed. But I'm wrong about that.... carbureted cars do have a nice steady air/fuel at idle perhaps, but they cannot adjust spark rapidly. So perhaps if we can "fix" those small rpm errors before they start rocking the boat, the idle will ultimately be much smoother than a carb car after all. And if the RPM error doesn't ever get much up over 50 or 75, it won't start hitting those large timing adjustments and swinging wildly.

So that's a new theory. But somehow that has to have a balance point still. And the stock RPM error timing numbers are rather large already. So what, we should make them larger at low rpm errors? From 5 - 7 degrees now up to 10 - 15 degrees? And what with the rest of the table over 200 rpms? Leave it as is?

FYI, for this part of the discussion, I don't want the ETC to be the factor.

[Sherman]

Ok I fixed it. Heres what I did...I doubled the enable rpms for both integral and proportional RPM error. Also, just as a "what if" I doubled my Min AFs so that they are now above what I was running last year with the non scaled tune..and it completely took care of the issue. No RPM dipping whatsoever whether im at idle, slowing down in neutral or using my transmission to slow me down. It does right to where its supposed to and stays there.

This WORKS!!!

Thank You Snyper, I have been working on this for weeks trying to figure it out.
This should be added to the How to section.

Sherman

[pontisteve]

Are you saying that because you scaled the tune (presumably to get around the injector size limitation in the PCM), that you also had to double your running airflow table?

I don't see how doubling the integral and proportional rpm error was necessary. Does it idle just fine if you didn't do that part?