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Old 06-29-2019, 10:12 AM   #101
Haive_Music
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Quote:
Originally Posted by james-30 View Post
My 19 still has the stumble only mine now happens rather engine is cold or warm. Anyway I have learned after starting if i wait 10 seconds or so then blurp the gas once I have no stumble. If i start and do nothing but let engine idol itll fall right on its face ie stumble to the point of damn near stalling.

I have decided to add a few more go fast parts before I get retuned. Going for 500whp stock type RA short block.
Haha, that's funny you mention the 'blip the gas thing' as I discovered that too, and it does the exact same thing on my end. If I blip the gas, no problem. If I don't, I'm 99% likely to have the issue happen.


As an update to my original post regarding this issue - my cold start stumble is definitely somewhat improved, but it's certainly still there.
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Old 09-17-2019, 02:08 PM   #102
Dwbarrett7
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Default I’ve tried this and no luck

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Originally Posted by Haive_Music View Post
Odd question, especially given the new years / low milage vehicles that exhibit this problem, but has anyone attempted trying to install a brand new front O2 sensor by chance?

I've been tempted to try it, but considering the car only has 12k miles on it, I doubt it went bad already, but...the problem does seem to happen right when the sensor begins reading.
I’ve tried this and no luck. Also tried deleting the air pump.
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Old 10-07-2019, 10:18 AM   #103
Dwbarrett7
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Default Problem 99% fixed

My tuner had my car for weeks for installation of a closed deck block and turbo upgrade. After installation he himself acknowledged the issue and was determined to solve it. I had very little faith considering many other tuners had the same issue and no one could resolve it. Anyway the problem is now 99% solved accept for a nano second of a slight stumble. Turns out it was in the tuning as suspected. What he changed I have no idea.
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Old 11-11-2019, 03:20 PM   #104
james-30
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So very interesting. I currently have my top mount, Cobb intake, and speed density all off the car as I'm installing ets front mount and matching intake then finally re tuned.

Anyway, while chasing an issue im having with my AEM oil gauge not working I started the car (parts mentioned above all uninstalled) to see if gauge would work. To my surprise my car experienced no cold start stumble what so ever. not even a hiccup. I haven't started car in couple weeks so block was room temp. Any ideas?
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Old 11-23-2019, 07:05 PM   #105
james-30
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^^Bump^^
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Old 11-23-2019, 11:16 PM   #106
mattminer
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2017+ STi's have a different logic than the earlier cars and as such when the SAI system is deleted they can experience starting issues under instances when the SAI system would have been active.

The information I have gathered from other tuning experts is as follows

"The ECU expects to see an altered behavior from the engine during air pump operation and "skews" accordingly with it. It expects for the O2 sensor reading to be changed when the pump is active, and it uses a different strategy to achieve proper fueling while that's occurring. Without the system plumbed correctly to the heads, that won't occur."


And this is directly from COBB

"Stumbling, stalling is common to 17+ STI with air pump delete. We do not recommend deleting that system for emissions, legal, and drivability reasons. Many Protuners have reported it and not deleting that system avoids this."
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Old 11-23-2019, 11:28 PM   #107
mattminer
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I have been able to mostly mitigate the issue by keeping open loop fueling active longer, but I know that's not 100% the correct fix.

I believe that most of the issues in this thread are the same (and some are other issues entirely)

I have cars here that have near identical mods and the only ones with this problem are SAI deleted.
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Old 12-11-2020, 09:50 AM   #108
mattminer
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Just a follow up, Ive fixed this on every car I had the issue with by reinstalling the easy half (driver side) of the air injection system. Hopefully one day Cobb will change their minds, but for now at least its known that it needs to stay. plumbed into at least one head.

WM
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