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Old 02-09-2018, 08:38 PM   #1
nathan.d.kim
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Default Extremely Negative AF Learning 1A only While Idling (2007 STI)

I searched multiple forums but could not find the same strange symptoms I am having on my IAG-tuned 2007 Subaru STI with various power mods (see list below). Plus, user support for the GD seems to be declining lately.

AF Learning 1A is usually around -15.0 to -21.
AF Learning 1B is 0.0 always.
AF Learning 1C is -0.10.

Overall AF Learning is -15.0 to -21 at idle/stop (1A+1B+1C).

If I give it any gas, the overall AF Learning is nearly zero when accelerating or WOT. At cruising, AF Learning is minimal also well below -8.0 (the acceptable value).

The only time the values are extreme is at a complete stop at idle. This shouldn't matter since AF really only matters when the car is under heavier loads (not at idle), right?

At cold start-up, the rpm occasionally hunts up and down at idle, but gets steady when the car is warmed up. Not always. Seems to be related to whether the HVAC is on - not 100% sure since it's intermittent.

I already pressure-tested the intake system post-MAF using my air compressor, boost leak tester, and soapy water. There is a slight leak where the BOV return line connects to my Perrin turbo inlet. The stock return line is stiff and connects at a slight angle to the metal tube on the inlet. Clamp is as tight as I can get it. I even replaced the stock line with a new one to see if that would help - negative.

Here are my power mods:
Rallispec forged shortblock (Wiseco)
Walbro 255
ID1000s
KS Tech 73-mm CAI
Perrin Turbo inlet (new, reinforced)
FP 71HTA turbo
PW TMIC
Cobb BPV
KillerBee ELH
Grimmspeed 2-bolt uppipe
Turbosmart 41-mm EWG
Cobb TBE
IAG-tuned with Cobb AP v3
Grimmspeed EBCS (2-port setup)
Omnipower 4-bar MAP
Denso MAF sensor (not Subaru OEM, but confirmed part number with Denso)
New OEM sensors (knock, front O2, rear O2)


I know this is a lengthy post, but I hope I am describing everything with enough detail that someone can help me out. I will eventually take it back to IAG if I can't figure it out, but thought I'd check with you all.

Thank you, community!
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Old 02-10-2018, 04:39 AM   #2
bobjr94
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Has it always been like that since it was tuned ?

An intake leak would show the a/f correction go the other way, like +15. How many grams / second if your af sensor showing at idle ? It should be 4-5 warm idle and 5-6 when the a/c or defrost kicks in. The MAF could going bad or just need to rescaled again in the 0-10 gm/second range to idle a bit leaner.

Also increasing the injector latency will make it idle leaner while not effecting the cruising/power af ratio very much. Or the minimum injector pulse width is set to large for those big injectors, so the ecu can't cut the fuel down any further then the fuel trim will max out. Also, what is the idle speed set to ? Maybe going up to 800 or 850 would help keep the mixture more even.

If the fuel pump duty cycle was turned up (as some people do with larger pumps) it can overload the fuel system (like idling at 60psi instead of 35).
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Old 02-10-2018, 09:04 AM   #3
nathan.d.kim
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Quote:
Originally Posted by bobjr94 View Post
Has it always been like that since it was tuned ?

An intake leak would show the a/f correction go the other way, like +15. How many grams / second if your af sensor showing at idle ? It should be 4-5 warm idle and 5-6 when the a/c or defrost kicks in. The MAF could going bad or just need to rescaled again in the 0-10 gm/second range to idle a bit leaner.

Also increasing the injector latency will make it idle leaner while not effecting the cruising/power af ratio very much. Or the minimum injector pulse width is set to large for those big injectors, so the ecu can't cut the fuel down any further then the fuel trim will max out. Also, what is the idle speed set to ? Maybe going up to 800 or 850 would help keep the mixture more even.

If the fuel pump duty cycle was turned up (as some people do with larger pumps) it can overload the fuel system (like idling at 60psi instead of 35).
I haven't checked the g/s yet but will do so and report back.

As far as the numbers after the tune, I don't remember anymore.

I got tuned last summer at IAG. Tried to email the outsourced tuner directly, but didn't get a reply. When I called IAG, they wouldn't schedule me on a tuning day because they think it is likely a mechanical issue. I'm a couple hours away but too busy with work to go there and have to go back again if tuning related. Thus, trying to rule out anything mechanical myself.

I think my idle speed is already around 800 to 900 rpm, but will check that also.

At the current state, any harm if the idle is that rich but normal under throttle?

I'll check those numbers again. Appreciate the advice.
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Old 02-17-2018, 02:30 PM   #4
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MAF reading is right around 5 g/s at warm idle. It's around 10 g/s for cold startup and drops as the engine warms up.

The idle hunting does not appear to be related to the HVAC as I thought. Random.

The MAF was replaced 6 months ago with Denso sensor, part number 197-6040.

Perplexed. Everything is fine except at idle... very rich.
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Old 02-17-2018, 05:31 PM   #5
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It just sounds like the maf scaling needs a bit more work in that area. Luckily, it doesn't really affect driving as it's so low in the maf range.
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Old 02-21-2018, 11:07 PM   #6
nathan.d.kim
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Perplexed even more. So, the weather was about 76 degrees today and the AF Learning 1A (idle) went back down to -2.6 to -4.0, which is within the acceptable range. Everything feels and looks great. Other posts I read have been saying that cold temperature shouldn't affect the AF Learning values.

I did send IAG some data logs when it was still around -14 AF Learning 1A. Hopefully, the tuner will take a look and see something.

Could this be caused by winter gas?

Only other thing I could think of is that I got a state inspection on Monday at a local shop. Did the mechanic fix a popped off hose or replace a vacuum cap during the inspection? Doubtful.
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Old 03-26-2018, 11:08 PM   #7
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Still having the issue, but the weird idle caused the car to die for a second. Started back up, struggled a bit, but smoothed out once again.

Just realizing that I have never cleaned the throttle body with 75k miles on the dash. It doesn't look that dirty, but reading other people with similar issues, the throttle body being grimy could affect the idle. This makes sense for my 2007 since it doesn't have an IACV. The throttle body is the only thing that controls the idle. Also, since the hunting idle is intermittent and not a problem at speed, I think a dirty throttle body is very likely.

Will clean out the throttle body this weekend and report back here.
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Old 03-28-2018, 12:29 PM   #8
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you are running pretty big injectors. do you have the low pulse width tables defined?

see this article for a better idea of what i'm taking about. Idle is the hardest for big injectors not properly scaled.

http://www.enginelabs.com/engine-tec...tion-with-fic/
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Old 03-29-2018, 01:15 AM   #9
nathan.d.kim
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Quote:
Originally Posted by anjuna View Post
you are running pretty big injectors. do you have the low pulse width tables defined?

see this article for a better idea of what i'm taking about. Idle is the hardest for big injectors not properly scaled.

http://www.enginelabs.com/engine-tec...tion-with-fic/
I don't know much about tuning or pulse widths. I got tuned at IAG but can't seem to get reach the tuner. Tried to email him directly and thru IAG without success...

I really haven't put many miles though a lot of months have gone by...

I will try to clean the throttle body, then see if I can get some sort of tuning adjustment.
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Old 03-30-2018, 12:43 AM   #10
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Well, cleaned the throttle body, but it wasn't that dirty at all. Pinched off the coolant lines and took the TB off to get a deep clean. I haven't driven it yet because it was late and the noise will piss off the neighborhood. I plan to burp the coolant system tomorrow and take the car to work in hopes that maybe the ECU will adjust. Doubtful.

I'll have to -
(a) See if the tuner can scale the MAF or injectors properly for me.
(b) Find a new tuner, or schedule a tuning adjustment with the same tuner.
(c) Do nothing and live with it.

Is it fair to rule out a vacuum leak since the AF Learning 1A (idle) is extremely negative?

I believe vacuum leaks usually show up as positive fuel trims.

Ugh - Wish I could scale my MAF myself and knew how to do it.
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Old 03-30-2018, 07:13 AM   #11
ShinjiML
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Quote:
Originally Posted by nathan.d.kim View Post
Well, cleaned the throttle body, but it wasn't that dirty at all. Pinched off the coolant lines and took the TB off to get a deep clean. I haven't driven it yet because it was late and the noise will piss off the neighborhood. I plan to burp the coolant system tomorrow and take the car to work in hopes that maybe the ECU will adjust. Doubtful.

I'll have to -
(a) See if the tuner can scale the MAF or injectors properly for me.
(b) Find a new tuner, or schedule a tuning adjustment with the same tuner.
(c) Do nothing and live with it.

Is it fair to rule out a vacuum leak since the AF Learning 1A (idle) is extremely negative?

I believe vacuum leaks usually show up as positive fuel trims.

Ugh - Wish I could scale my MAF myself and knew how to do it.
Did the tuner lock your map? Are you able to open your rom in ATR (if you have ATR)?
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Old 03-30-2018, 08:12 AM   #12
nathan.d.kim
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I'm assuming the map is locked, but will check tonight after work.
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Old 03-31-2018, 05:47 PM   #13
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Tried to download AccessTuner, but now you have to pay $149 and finish EFI University training to start using it. Not thrilled that a free app is now pay-walled by Cobb. I understand people like me who have no tuning knowledge should be careful with modifying a map, but - heck - I'd like to have the freedom to grenade my engine if my heart desires. $149 is steep.

Any other way to tell if the map is locked?

I did, fortunately, get a new MAF sensor right before the tune. It was the Denso one that was confirmed fitment by part number for my car ($120 versus the OEM $270).

Anyway, quick update: After cleaning the throttle body and burping the coolant system (from TB removal), the AF Learning 1A (idle) value is down to about -9.7 after a 15 minute drive. Remember it was -14 to -17 before. I'll have to put some more miles on it for the fuel trim to adjust, but if this causes the idle value to get down to an acceptable range, that would be purely awesome. If the hunting idle also goes away, even better.

Will put some more miles on the car over the next few days and see what happens.
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Old 04-18-2018, 12:13 AM   #14
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I only drive this car about 1x a week (or less), so the updates are not frequent.

So, after I cleaned the drive-by-wire throttle body and drove the car for a bit, the AF Learning 1A (idle) parameter went down to -1 to -3, which was great. I thought the problem was solved. However, the weather at the time was about 75-80 degree outside (similar to when I got protuned).

The temperature dropped these past few days to about 45 or less. I drove the car about 12 miles and the AF Learning 1A (idle) parameter went back to about -11. So, the AF Learning 1A at idle seems to be related to the air temperature. I bet if the temperature goes back up to 75 or so, the value will go back to about -3.

If the air is colder outside and more dense, shouldn't the ECU be adding fuel to avoid a lean condition? Not sure why it is pulling so much fuel at idle.

I know, I know. "Contact your tuner." I've tried numerous times (3) now including through the vendor. No luck at all - no response.

I also can't scale the MAF myself b/c the new version of AccessTuner requires payment and training... and I also don't know how to do anything like that.

Is it time for a new tune? Is there anything else I should consider first?

I have used my air compressor to charge the system with pressurized air. I was not finding any leaks while pushing about 20 psi through the turbo inlet. It doesn't seem to be leak-related. The values were back to the same range when the weather was similar to the day I got tuned.

Such a shame since I only have about 2,000 miles on the current tune (though it was 9 months ago).

Last edited by nathan.d.kim; 05-05-2018 at 01:20 AM.
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Old 05-05-2018, 01:21 AM   #15
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Tuner got back to me and was able to adjust the tune. Now that the weather is hot, the AF Learning 1A on the new map is showing positive values.

I switched back to the first map and numbers are good for hot weather (around -2).

I think I'll use map 1 for summer and map 2 (new one) for winter or cold weather.

Very strange. Didn't think temp should affect the tune at idle but it seems to vary quite a bit. We have had crazy temperature swings though... 50 to 95... 45 degree differential.
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Old 05-07-2018, 11:46 AM   #16
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This is because of the low pulse width. promiiiiiiiise.

idle with big injectors is hard. like, real hard.

think of it this way - you have a 10lb sledgehammer (big injectors) for all the work you need to do.

So if you just needed to nail in a tiny nail (idle fueling), it would be hard.
If you needed to take down a wall (WOT) it would work perfect.

Yes, the temperature of the air changes g/rev (MAF) because colder air is more dense. Colder air needs more fuel, so the not-so-linear portion of the latency table that is being called on moves.
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Old 05-07-2018, 11:57 AM   #17
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Thanks for the explanation.

Why negative fuel trim though?

If cold air needs more fuel, why is the ecu removing fuel rather than adding?

Just wanting to learn.
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Old 05-07-2018, 12:49 PM   #18
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probably because that area is non-linear.

There's a "minimum" pulse width for your injectors. it's the physical limitation where you cannot open and close the injector any faster. This means you have a "minimum" amount of fuel that you can inject. Sometimes even that minimum can be too much.

Additionally, if your values aren't set quite right, you can end up over injecting or under injecting in the non-linear area.

This is a REALLY good article. http://www.enginelabs.com/engine-tec...tion-with-fic/

Basically, if you have this sort of issue, driveability suffers as well, as you'll transition from A to B fuel trim and things get ****ty.
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Old 05-12-2018, 04:40 PM   #19
nathan.d.kim
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Off topic on my own thread: Will my 2007 STI stock headers fit in a 2008 WRX (2.5 turbo, non-STI)?

Potential buyer, but not sure if it works. Seems there may be an oil cooler/filter fitment issue...
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Old 11-12-2020, 12:19 PM   #20
currancchs
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Default Had similar issue

I had a similar issue which appears to have been throttle-body related. After cleaning, things were much improved, but still somewhat problematic at full hot idle (but in fuel control as opposed to three points rich!). I found that the problem occurred only at throttle opening angles of 1.96% or less, which, for me, only occur at full hot idle (throttle is more open, about 2.75%, even at 170 coolant temps and 700rpm idle) post cleaning (was happening at 2.5% and below before). Honestly, I think my TB may still be a bit dirty and a more thorough cleaning might further improve things or even completely resolve them.

The target idle throttle opening angle can be adjusted in the tune and bumping it up slightly may help in your case. Monitoring this parameter may also show a correlation between your issue and throttle opening angle, confirming the issue.

You may also want to check fuel pressure. I am running the same fuel pump (Walbro 255lph) on a 2006 WRX TR and noticed fuel pressure about 10psi high that changing the regulator to a new OEM one resolved. This can also cause a rich idle/surge if the base pressure is high enough (not the root cause in my case though, but perhaps a contributing factor).

A discussion of my issue, with maps/logs, can be found here: https://forums.nasioc.com/forums/sho....php?t=2929176 and here: https://www.romraider.com/forum/view...p?f=15&t=17722

A video of my issue, including the issue going away when AC was engaged at a full, hot idle, can be found here: https://studio.youtube.com/video/cVziOiY7E90/edit

Also, I know this thread is old. This post is more for anyone who may have run across this post while searching these symptoms than for the OP.

Last edited by currancchs; 11-23-2020 at 02:12 PM. Reason: Add link to my related thread
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Old 11-17-2020, 12:23 PM   #21
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Quote:
Originally Posted by currancchs View Post
I had a similar issue which appears to have been throttle-body related. After cleaning, things were much improved, but still somewhat problematic at full hot idle (but in fuel control as opposed to three points rich!). I found that the problem occurred only at throttle opening angles of 1.96% or less, which, for me, only occur at full hot idle (throttle is more open, about 2.75%, even at 170 coolant temps and 700rpm idle) post cleaning (was happening at 2.5% and below before). Honestly, I think my TB may still be a bit dirty and a more thorough cleaning might further improve things or even completely resolve them.

The target idle throttle opening angle can be adjusted in the tune and bumping it up slightly may help in your case. Monitoring this parameter may also show a correlation between your issue and throttle opening angle, confirming the issue.

You may also want to check fuel pressure. I am running the same fuel pump (Walbro 255lph) on a 2006 WRX TR and noticed fuel pressure about 10psi that changing the regulator to a new OEM one resolved. This can also cause a rich idle/surge if the base pressure is high enough (not the root cause in my case though, but perhaps a contributing factor).

A discussion of my issue, with maps/logs, can be found here: https://forums.nasioc.com/forums/sho....php?t=2929176 and here: https://www.romraider.com/forum/view...p?f=15&t=17722

A video of my issue, including the issue going away when AC was engaged at a full, hot idle, can be found here: https://studio.youtube.com/video/cVziOiY7E90/edit

Also, I know this thread is old. This post is more for anyone who may have run across this post while searching these symptoms than for the OP.
Update: Changing this setting in my map did not improve my situation. If anybody has any input on this issue, I'd love to hear it!
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