Return-to-Idle Issues - Please Help!

Looking on input for return-to-idle issues. 6.0L/M6, 231/239 .62x lift, fast 102, 799 cnc ported heads. 896 PO1 PCM. Engine wants to die when car is rolling and I let off the throttle. In the log, you can see identical situations at 4:15 (engine tries to die) and 4:58 (engine returns to idle perfect). Everything is virtually the same including IAC, timing, AFR, map, MAF, cylinder air mass.

STFT higher at 4:15, injector pulse width @3.4 vs 2.9 @ 4:58. Please have a look and give guidance.

First thing I'd do is start with a different OS that has the rest of the rolling idle tables. Unless you have unlimited licensing you'll need to license it again.

Start with this then swap over all your critical calibration tables and params. Do a write entire then you'll have a fully functioning rolling idle OS that when tuned properly will cure most all your return to idle problems.

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Originally Posted by Aggie3rdGen

Looking on input for return-to-idle issues. 6.0L/M6, 231/239 .62x lift, fast 102, 799 cnc ported heads. 896 PO1 PCM. Engine wants to die when car is rolling and I let off the throttle. In the log, you can see identical situations at 4:15 (engine tries to die) and 4:58 (engine returns to idle perfect). Everything is virtually the same including IAC, timing, AFR, map, MAF, cylinder air mass.

STFT higher at 4:15, injector pulse width @3.4 vs 2.9 @ 4:58. Please have a look and give guidance.

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Almost always a dip returning to idle has to do with a rich decel. In all but one of the idle dips I saw in your log your wideband was coming back with a 13.4:1 or richer. Sometimes the decel area of the VE has to be done by hand and not by AFR or LT error. But even just using AFR error would get you closer than you are now.

Also.. you have too much base idle timing. I'd shoot for 18 degrees normal in this setup. YES at 25 degrees it idles easier.. but what you want is to save up some "reserve torque" So if your airflow (will take more) is setup to support 18 degrees of timing.. if the idle should dip.. you could go to 25- up to 28ish to save the idle.

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Originally Posted by edcmat-l1

First thing I'd do is start with a different OS that has the rest of the rolling idle tables. Unless you have unlimited licensing you'll need to license it again.

Start with this then swap over all your critical calibration tables and params. Do a write entire then you'll have a fully functioning rolling idle OS that when tuned properly will cure most all your return to idle problems.

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I've been strongly considering this. I've never done a segment swap, but it seems everyone uses the 0411 - 12212156 OS. This OS will segment swap into my 896? I just need the engine section, correct? Is the segment swap the same as a write entire, as you've mentioned? Appreciate the feedback and file.

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Originally Posted by Alvin

Almost always a dip returning to idle has to do with a rich decel. In all but one of the idle dips I saw in your log your wideband was coming back with a 13.4:1 or richer. Sometimes the decel area of the VE has to be done by hand and not by AFR or LT error. But even just using AFR error would get you closer than you are now.

Also.. you have too much base idle timing. I'd shoot for 18 degrees normal in this setup. YES at 25 degrees it idles easier.. but what you want is to save up some "reserve torque" So if your airflow (will take more) is setup to support 18 degrees of timing.. if the idle should dip.. you could go to 25- up to 28ish to save the idle.

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Thanks for the input, Alvin. I'll look to keep refining the VE tables, especially in the deceleration zones. By chance, have you noticed this is true when running a MAF tune as well? Curious if the linear table of the MAF knows when the engine is in decel.

For the base idle timing, I'll try backing it down, as you suggested. If I recall, when trying this before, it would struggle to stay idling and die, but I'll try increasing idle airflow here.

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Originally Posted by Aggie3rdGen

I've been strongly considering this. I've never done a segment swap, but it seems everyone uses the 0411 - 12212156 OS. This OS will segment swap into my 896? I just need the engine section, correct? Is the segment swap the same as a write entire, as you've mentioned? Appreciate the feedback and file.

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They're different OSs you can't segment swap them. You have to start with 2 files with the same OS to be able to do a segment swap.

You need to do as I said and start with that file, modify it with your base tables then do a write entire. A write entire is the only way to change the OS.

The GEN3 PCMs when you run them in hybrid (MAF/VE) they do reference the VE heavily during pedal transitions. First thing to do is get it to run as best as possible in SD then move on the dialing in the MAF.

The rolling idle tables work as a dash pot to keep the RPM above idle speed while you're moving. This keeps it from trying to go right back to idle and then the subsequent oscillations.

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Originally Posted by Aggie3rdGen

Thanks for the input, Alvin. I'll look to keep refining the VE tables, especially in the deceleration zones. By chance, have you noticed this is true when running a MAF tune as well? Curious if the linear table of the MAF knows when the engine is in decel.

For the base idle timing, I'll try backing it down, as you suggested. If I recall, when trying this before, it would struggle to stay idling and die, but I'll try increasing idle airflow here.

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Tuning VE with that cam is going to be critical. You'll likely get a better result in strict SD mode anyway.

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Originally Posted by Alvin

Tuning VE with that cam is going to be critical. You'll likely get a better result in strict SD mode anyway.

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I agree. I'd run that in speed density.