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Old 03-29-2021, 01:52 PM   #1
Compelica
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Getting the ECU to quickly learn idle stability after a reflash

Figured that it would be applicable to post this here in the Software Tuning section as we deal with these issues more often.

After a reflash the ECU takes some time to relearn fuel trims, and those trims learn completely after a consistent amount of driving. But idle stability was one thing I could never predict - it would take a varied amount of time to get the idle to stop hunting with the AC on, and the RPMs would do engine shuddering dips after rising upon a slight tap on the throttle.

So I came across this extended OBD2 PID called 'Deposit Loss Flow'. As a background - the throttle body has carbon deposits caked onto the walls or onto the butterfly valve which impedes air flow. As a result, the TB must compensate with a larger opening to maintain the target idle speed. It is solely my guess here but the throttle body can easily adapt its opening during extended idle but it has to learn this position on where to 'settle' during rapid movements of the throttle.

Upon a reflash, this PID value would always be 0 grams per sec, indicating there is no compensation (subsequently opening of TB) done. 500 kilometers of driving and it still showed 0. Which then I found this particular bit in another Toyota service manual:



And it works. Followed the procedure to the dot, and right after the last step after starting the engine the learned values finally came up and my idle smoothened out. I'm happy once again

Also, be sure to do this procedure without the AC on. Also you would want the idle to be as stable as possible during the warm up period so turning off lights and head unit may probably help. Hope this works for you guys trying to fix your idle
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Old 03-29-2021, 02:19 PM   #2
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Quote:
Originally Posted by Compelica View Post
Figured that it would be applicable to post this here in the Software Tuning section as we deal with these issues more often.

After a reflash the ECU takes some time to relearn fuel trims, and those trims learn completely after a consistent amount of driving. But idle stability was one thing I could never predict - it would take a varied amount of time to get the idle to stop hunting with the AC on, and the RPMs would do engine shuddering dips after rising upon a slight tap on the throttle.

So I came across this extended OBD2 PID called 'Deposit Loss Flow'. As a background - the throttle body has carbon deposits caked onto the walls or onto the butterfly valve which impedes air flow. As a result, the TB must compensate with a larger opening to maintain the target idle speed. It is solely my guess here but the throttle body can easily adapt its opening during extended idle but it has to learn this position on where to 'settle' during rapid movements of the throttle.

Upon a reflash, this PID value would always be 0 grams per sec, indicating there is no compensation (subsequently opening of TB) done. 500 kilometers of driving and it still showed 0. Which then I found this particular bit in another Toyota service manual:



And it works. Followed the procedure to the dot, and right after the last step after starting the engine the learned values finally came up and my idle smoothened out. I'm happy once again

Also, be sure to do this procedure without the AC on. Also you would want the idle to be as stable as possible during the warm up period so turning off lights and head unit may probably help. Hope this works for you guys trying to fix your idle

Interesting, so this procedure is like a band aid if you have a dirty throttle valve.

If you have to go through this procedure, and it actually works, you now know your throttle valve is probably dirty, wouldn't it be a good idea at this point to just disassemble and clean the throttle body and valve, then reset the ECU?
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Old 03-29-2021, 02:39 PM   #3
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Interesting, so this procedure is like a band aid if you have a dirty throttle valve.

If you have to go through this procedure, and it actually works, you now know your throttle valve is probably dirty, wouldn't it be a good idea at this point to just disassemble and clean the throttle body and valve, then reset the ECU?
Good observation - I was thinking of this as well, so I pulled out the intake tubing and inspected TB before doing the procedure. It was reporting around 2.3gram/sec loss the last time, and I wanted to see if cleaning the TB would further reduce the flow loss.

However my TB was basically spotless apart from the dye markings and a very light layer of dust, though I suppose there would always be some form of compensation made out for differences/variations.

There probably isn't any perceptible performance loss either - given that at around WOT the engine is taking in 143g/s, a 2.3g/s loss is slightly less than 2% which is negligible when calculated by the ECU as a load.
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Old 03-29-2021, 05:07 PM   #4
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Originally Posted by Compelica View Post
Good observation - I was thinking of this as well, so I pulled out the intake tubing and inspected TB before doing the procedure. It was reporting around 2.3gram/sec loss the last time, and I wanted to see if cleaning the TB would further reduce the flow loss.

However my TB was basically spotless apart from the dye markings and a very light layer of dust, though I suppose there would always be some form of compensation made out for differences/variations.

There probably isn't any perceptible performance loss either - given that at around WOT the engine is taking in 143g/s, a 2.3g/s loss is slightly less than 2% which is negligible when calculated by the ECU as a load.
So what was your g/s loss that the PID was finally reporting as after you cleaned the TB and then after you performed the re-learn once again?
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Old 03-29-2021, 09:54 PM   #5
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So what was your g/s loss that the PID was finally reporting as after you cleaned the TB and then after you performed the re-learn once again?
Left it alone as there was nothing to clean

Was surprised myself as I was coming to about 100k KM and I expected some dirt there but clean as a whistle.

Last edited by Compelica; 03-29-2021 at 10:04 PM.
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Old 03-29-2021, 10:58 PM   #6
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something tells me it's some closed loop calculation similar to the various LTFT it learns
Like, maybe it's something calibrated against the original maf scaling, and that % calculation is probably just added up after a while to try correct some wild fuel trim that the ecu wants not to see
I don't think the ecu really knows how much debrees is present in the wall of the throttle body.

Whatever it is we haven't control of it in romraider or ecutek, so it's definitly something annoying in custom tuning
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