Idle surging once car comes to complete stop...

[Snyper]

Tune and log posted. At first I was getting the dipping all the time...once I dialed in my idle airflows I had to add to them to prevent it from dipping while slowing down. I have my idle speeds set to 1200 all the way down to 3mph then it goes back down to 800 once im stopped-which is when I have the issue. The second the car is completely stopped the timing jumps all over the place for a little while until it will eventually find itself. Any ideas on why this would do this? As you can see in the log posted while slowing down everything is fine until the speed reaches 0. This is an OLSD 50% tune. Also, can someone tell me why my DFCO isn't working?

[pontisteve]

Personally, I believe that when you have a big cam, the idle over/underspeed tables need to be desensatized in the first 150 rpm. Otherwise, the computer will take the normal rolling idle a camshaft gives, and try so hard to correct it that it shoots timing all over the place trying. And that leads to speed increases/decreases and causes idle hunting.

To prove the theory, you could zero out the idle over/under speed tables entirely, or at least for the first couple hundred rpm and see if that helps.

If you are sitting there idling and it's hunting, try using the scanner to lock the timing to a steady number like 18, and see if stabilizing the idle timing stabilizes the idle.

Another thought... your idle spark tables are different than your normal spark tables. So if your speed reaches 0 and suddenly you have problems, maybe it's because you suddenly hit the idle tables, and it's likely the timing suddenly dropped way down, causing a sudden drop in RPM and then the PCM starts fighting to correct this via the over/under tables.

[Snyper]

Okay, I made a few changes to the tune like taking away some over/under I matched the hi/lo octane tables to the idle base and made a few other changes. The more that goes wrong the more I seem to learn..so this is a good thing.

[DSteck]

Personally, I believe that when you have a big cam, the idle over/underspeed tables need to be desensatized in the first 150 rpm. Otherwise, the computer will take the normal rolling idle a camshaft gives, and try so hard to correct it that it shoots timing all over the place trying. And that leads to speed increases/decreases and causes idle hunting.

To prove the theory, you could zero out the idle over/under speed tables entirely, or at least for the first couple hundred rpm and see if that helps.

If you are sitting there idling and it's hunting, try using the scanner to lock the timing to a steady number like 18, and see if stabilizing the idle timing stabilizes the idle.

Another thought... your idle spark tables are different than your normal spark tables. So if your speed reaches 0 and suddenly you have problems, maybe it's because you suddenly hit the idle tables, and it's likely the timing suddenly dropped way down, causing a sudden drop in RPM and then the PCM starts fighting to correct this via the over/under tables.

If anything, you need to tighten the control band. That's how I tame huge cams and engines with very light clutches.

[Snyper]

I made some changes and now its even worse.

[Snyper]

I went back to where I was originally and now at start up it idles fine...but still surges at idle once the car comes to a complete stop. And if you look at the idle log I attached..at 45 seconds in the VCM controls I turned the idle spark ON(off) and as soon as I did it started surging pretty bad. Ive tried the method made to get the final air flows correct and I had to add about 30% instead of removing 20% in order to get it to idle correctly....what would cause the idle surging once the idle spark is turned off?

[Mez]

I'll give it a shot. If it does not work, oh well it did not cost you anything.
I believe it will never go into closed loop. Is that your goal? Many tables have been changed but I don't understand the logic behind it.

1. Minimum airflow table. Add .15 below 1400 rpm.

2. I don't understand your VE or ignition advance tables at all. Where did you get them? Your VE table is much lower thank stock. Since you are running without a MAF, this is critical to have right. Same with your timing table. Try changing them back to stock.

3. Idle proportional and integral. Return to stock.

4. Idle RPM min. Set minimum idle table to 800 rpm at 0 mph.

5. Spark Over/Under speed tables. Set back to stock but cut in half at 64 rpm and below.

6. If you are using E10 gas, change stoich to 14.3.

[DSteck]

I'll give it a shot. If it does not work, oh well it did not cost you anything.
I believe it will never go into closed loop. Is that your goal? Many tables have been changed but I don't understand the logic behind it.

1. Minimum airflow table. Add .15 below 1400 rpm.

2. I don't understand your VE or ignition advance tables at all. Where did you get them? Your VE table is much lower thank stock. Since you are running without a MAF, this is critical to have right. Same with your timing table. Try changing them back to stock.

3. Idle proportional and integral. Return to stock.

4. Idle RPM min. Set minimum idle table to 800 rpm at 0 mph.

5. Spark Over/Under speed tables. Set back to stock but cut in half at 64 rpm and below.

6. If you are using E10 gas, change stoich to 14.3.

A lot of the stuff you are suggesting he change are part of scaling a tune.

[Snyper]

Ok so far this is the best tune ive had in the car. I went back a few tunes and sort of started back at square one. It idles very steady (I followed the min. airflow method and its a lot less than what I had previously) the car idles very well now however when downshifting and I push in the clutch the car will start to dip then stall...if I put the car in neutral before I start to slow down it will go down to idle and stay there....

[Snyper]

I'll give it a shot. If it does not work, oh well it did not cost you anything.
I believe it will never go into closed loop. Is that your goal? Many tables have been changed but I don't understand the logic behind it.

1. Minimum airflow table. Add .15 below 1400 rpm.

2. I don't understand your VE or ignition advance tables at all. Where did you get them? Your VE table is much lower thank stock. Since you are running without a MAF, this is critical to have right. Same with your timing table. Try changing them back to stock.

3. Idle proportional and integral. Return to stock.

4. Idle RPM min. Set minimum idle table to 800 rpm at 0 mph.

5. Spark Over/Under speed tables. Set back to stock but cut in half at 64 rpm and below.

6. If you are using E10 gas, change stoich to 14.3.

Yeah, im running a 50% scaled tune so everything is as it would be doubled. As far as spark over/under 64-0 or 64-512? Im not sure what im missing. When running the previous tunes the car idles like shit but when I push the clutch in during coast down it goes right to idle and stays...and with this current tune it does the opposite(but is much more dealable and the tune is much cleaner) Min airflow tables were found using 5LEs method...but instead of taking away 20% from the numbers the scanner spit out, I actually had to add 30%. So they are increased.

[Mez]

I am out of my league.

[Snyper]

If you look at the log..(I could be wrong) but it looks like it could be the over/under. It seems like the car goes over a little bit and then it KILLS timing(from 17 to 6..which is set in one of the tables) and then the rpms go under so it tries to re-correct itself. I went in and cut all the OVER tables completely in half...so where its cutting 11 its now cutting 5.5..Im going to see if that makes it a little better. If it doesn't im pretty much out of ideas.

[pontisteve]

Dsteck, perhaps you could elaborate for me? Im going under the theory that if a cam won't idle perfectly smooth, we shouldn't make it try to, or we just end up in an increasing over/under speed situation where timing fluctuates. This theory is based on cars idling wildly, but when locking the timing (via the scanner), the idle stabilizes.

I figure we can use the over/under tables, but just desensatize them under 150 rpm error. This also assumes that the idle airflow is already pretty correct.

Perhaps Dsteck, if you could be a little more specific on how you approach this? Am I correct to assume that in either case, the over/under tables is the key?

[edcmat-l1]

Haven't looked at the tune or logs, but knowing what I know about those systems, you need to lighten up on the overspeed park tables, above like 128 RPM. What happens on decel, is the overspeed spark table pulls a whole bunch of timing out to get the engine to decelerate rapidly, and it can cause a stall (coastdown table mainly)

Using the overspeed spark table, you can control the deceleration of the engine.

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.

[DSteck]

With big cams, I have spark correction maxed out by 100rpm error. A huge cam isn't going to want to idle rock steady like a stock cam, so over and under speed error needs to be rectified quickly. I have tried the dead band approach, and it just makes idle swing even more. Timing will get jumpy as hell with really aggressive over and under speed, but the idle speed won't fluctuate too far from commanded idle speed. I also only use a maximum of about 12-15* for correction instead of 22 like some stock setups use.

[edcmat-l1]

With big cams, I have spark correction maxed out by 100rpm error. A huge cam isn't going to want to idle rock steady like a stock cam, so over and under speed error needs to be rectified quickly. I have tried the dead band approach, and it just makes idle swing even more. Timing will get jumpy as hell with really aggressive over and under speed, but the idle speed won't fluctuate too far from commanded idle speed. I also only use a maximum of about 12-15* for correction instead of 22 like some stock setups use.

That's basically the way I set them up. Timing "All in" by less than 100 rpm in the spark tables. When you're real close on the A/F and base idle airflow table, the timing swing is less severe. Also, slowing down the rate at which the throttle blade wants to control idle helps too.

[Snyper]

Can you elaborate more on this? You want high over/under spark numbers from 0-112rpms and less from 128-512? Also, how do you slow down the throttle blade on an E40? It seems like that would help.....heres my over/under tables

[DSteck]

That's basically the way I set them up. Timing "All in" by less than 100 rpm in the spark tables. When you're real close on the A/F and base idle airflow table, the timing swing is less severe. Also, slowing down the rate at which the throttle blade wants to control idle helps too.

Yep. Amazing how correct injector data makes them idle tons smoother too. My buddy just got his 441 LS7 running, and it has ID850s. Dead nuts idle at stoich.

Since timing is the quickest responder, that's why I rely on for most of the idle control (assuming fuel is correct).

[Snyper]

I just noticed something(not sure if this could be the cause) but for whatever reason the Idle overspeed(#5) I have it adding 7* and I think it should be -7 not +7...I just went back a couple of tunes and noticed this was still in the negatives..maybe that would be whats throwing everything off?

[Snyper]

Yep. Amazing how correct injector data makes them idle tons smoother too.

Since timing is the quickest responder, that's why I rely on for most of the idle control (assuming fuel is correct).

I completely agree with you. I was running 83# injectors all last year with the wrong data and you should of seen my VE table. I just recently corrected it and since doing so the completely shape of the VE table changed(looks normal now), my cam almost sounds stock, and the low cruise super lean issue I was having went completely away.