Idle dropping too low
Thread Starter
TECH Apprentice
Joined: Jul 2012
Posts: 341
Likes: 12
From: UK
Idle dropping too low Hi,
Never been able to nail this problem but worse in colder weather and until 80 deg c.
If i start the car starts well but idle dips and take hold.
LS1 224r cam 90mm Holley cable TB 241 heads, no MAF SD only COS 3 Efilive with oxygen feedback in idle and part throttle Semi closed loop
Ive put up with it so far and its time to have a play with it.
If i blip throttle before i get to 80 deg C plus the idle dips down to 600 rpm ish but this is with Idle tips and tricks done, like increasing spark bump in lower than idle RPM etc etc.
Do i need more desired air flow? It is a pain to reverse or drive up to temperature and even then from logs the idle still drops a little when warm.
Attached is warm up log and current tune
Any help greatly appreciated
regards
Gav
Never been able to nail this problem but worse in colder weather and until 80 deg c.
If i start the car starts well but idle dips and take hold.
LS1 224r cam 90mm Holley cable TB 241 heads, no MAF SD only COS 3 Efilive with oxygen feedback in idle and part throttle Semi closed loop
Ive put up with it so far and its time to have a play with it.
If i blip throttle before i get to 80 deg C plus the idle dips down to 600 rpm ish but this is with Idle tips and tricks done, like increasing spark bump in lower than idle RPM etc etc.
Do i need more desired air flow? It is a pain to reverse or drive up to temperature and even then from logs the idle still drops a little when warm.
Attached is warm up log and current tune
Any help greatly appreciated
regards
Gav
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Joined: Aug 2010
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From: Ann Arbor, MI
I don't know EFI, but in HP Tuners, there is a "Min TPS" setting, e.g 1.2% below which it switches from the main spark tables to idle spark tables. The Idle spark tables default to a fixed value, around 20 degrees, for all idle RPM and MAP values. This helps maintain a stable idle. However in the main table, the advance drops from e.g. 20 degrees at 800 RPM to 5 degrees at 400 RPM. So, if your TPS at idle were to read e.g. 2%, it would use the main advance table which is troublesome - as your RPM drops a bit (eie. cam lope), the advance would quickly drop, dropping your idle speed further, etc. Things like the Adaptive Idle Underspeed would compensate but only so much. This could drop your idle to a much lower value than desired and/or give you an unstable idle.
I'm certainly not a tuning expert, but to solve, I simply set a constant advance in the idle RPM ranges in both the main and idle advance tables. This way the advance doesn't jump all over the place as you come down to idle to lightly accelerate from idle.
If you decide to take this approach, set the timing before you change the base idle airflow as the amount of advance changes how much idle airflow is needed.
I'm certainly not a tuning expert, but to solve, I simply set a constant advance in the idle RPM ranges in both the main and idle advance tables. This way the advance doesn't jump all over the place as you come down to idle to lightly accelerate from idle.
If you decide to take this approach, set the timing before you change the base idle airflow as the amount of advance changes how much idle airflow is needed.
Teching In
Joined: Apr 2023
Posts: 15
Likes: 0
From: Palo Alto, CA
Yeah I agree with this as well. If not already done, you want your idle spark and main spark table to roughly match up so that when it transitions to idle it won't excessively drop spark.
Last edited by v1.5; Apr 27, 2023 at 08:27 PM.
Thread Starter
TECH Apprentice
Joined: Jul 2012
Posts: 341
Likes: 12
From: UK
Thanks,
My basespark and high are all set the same anyway.
My counts were as 40 to 60 but need to recheck.
My LS swap does have a turbo and I have no clutch peddle switch (guess it thinks it's always in gear?)
regards
gav
My basespark and high are all set the same anyway.
My counts were as 40 to 60 but need to recheck.
My LS swap does have a turbo and I have no clutch peddle switch (guess it thinks it's always in gear?)
regards
gav
Thread Starter
TECH Apprentice
Joined: Jul 2012
Posts: 341
Likes: 12
From: UK
Upped the g/s by 2 ish and now can drive it ok as it's warming up. In fact revs hanging a bit now and reluctance to drop to my target 950 at normal temp. Will try decreasing cells at operating temp a bit.
regards
gav
regards
gav
TECH Fanatic
Joined: Oct 2014
Posts: 1,220
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From: Virginia
I did a video on this awhile ago based on some knowledge I gained from some awesome tuners out there. Theres some math you can plug in to actually adjust your IAC. Yes, it’s a pain in the ***, but worth the 30 minutes to an hour you might spend on it if you’re looking for great manners.
Also, there is another way of plotting idle airflow for your BRAF table, and that’s using dynamic air. I know, Russ K is awesome and all, but technically idle desired is a result of BRAF and IAC. So.. Personally I log dynamic air, plug that on the BRAF, then mess with the IAC table. Read the descriptions at the bottom to get a better idea.
TECH Fanatic
Joined: Oct 2014
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From: Virginia
It’s just splitting hairs, but on the Gen III PCMs it’s “Base running airflow” so, BRAF lol. Also check your throttle set screw adjustment too. They do get loose occasionally and no amount of tuning will help if the blade isn’t where it needs to be. Make sure when adjusting that to watch your TPS voltage. Iirc it cannot exceed 0.7 volts otherwise the PCM thinks you’re on the throttle and kills the idle routines.
Registered User
Joined: Apr 2024
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It’s just splitting hairs, but on the Gen III PCMs it’s “Base running airflow” so, BRAF lol. Also check your throttle set screw adjustment too. They do get loose occasionally and no amount of tuning will help if the blade isn’t where it needs to be. Make sure when adjusting that to watch your TPS voltage. Iirc it cannot exceed 0.7 volts otherwise the PCM thinks you’re on the throttle and kills the idle routines.
I used all of your videos on youtube to get my gto to idle and iac to work. You do any remote tuning or assistance on stubborn ones? I’ve got a few annoying hiccups with it still. Let me know thanks!