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Old 02-16-19, 04:16 PM   #1
haive_music
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Default Cold start stumble after 20 seconds

Hey Guys,

I've been trying to track down this issue and have I've no luck discovering what it is. I can't even get my tuning shop to give me a call back and work toward a resolution either, so I'm hopeful someone has some insight.

I just got my 2017 STI tuned, and there were no issues with it on the dyno. Tune came out great, except for when I got it home the next morning and realized that it has a cold start stumble every morning now. It only happens when it's cold for some reason. The car starts up perfect, idle is great, then literally after 20-22 seconds, the car bogs down and it nearly dies. This goes on for about 3-5 seconds, then the car corrects itself, and it goes back to idling perfectly fine. Hot idle is perfect. Drivability is great. Car made great power. No other issues or CELs with the vehicle. No idea what's causing this.

I have seen a few other random references to this same issue on 2016-2018 model STIs for some reason. I don't know if this is a change in the ECU or how they are tuned? Anyone have any ideas? I'm suspecting this has something to do with the TGV delete, but, those have been being removed on these engines for how many years now without issue. I have also verified the functionality of the stock baro sensor - it is still plugged in and working.


Car has only 10k miles on it, and runs only 93 fuel, compression test came out great when I checked it. Mod list as follows: IAG air pump delete, IAG tgv delete, Cobb intake + box, Cobb turbo inlet, Cobb upppe, Cobb downpipe + full catback exhaust, Perrin EHL, Cobb EBCS, Cobb 20g turbo, Cobb fuel rails, Cobb fuel injectors (1050), Cobb FPR kit, Cobb parallel fuel line kit, AEM fuel pump, Cobb AOS, and Cobb FMIC. I think that's about it.



Assuming I can even manage to get ahold of them, can I somehow get my tuner to unlock my map so I can maybe find anther tuner to look at it? This is my first Subaru since my old 2004 WRX (which was open source). A lot has changed since my last experience.

Thanks in advance. Appreciate it.

Last edited by haive_music; 02-16-19 at 04:21 PM.
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Old 02-17-19, 04:21 AM   #2
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Default Re: Cold start stumble after 20 seconds

This does sound like a tunning issue in my opinion. The car operates great besides a brief cold start idle stumble. Your tuner should be able to correct this and possibly could even correct this without you having to come back in. I believe someone else on here was experiencing the same thing recently and it was just a simple table/parameter adjustment in the tune if i remember correctly.

Now here is my gripe with this whole thing. You just spent the money to get the car protuned somewhere and they wont even give you the courtesy of returning your phone call?? That doesnt sound right to me. How much time has elapsed since you have tried contacting them? I would try giving it a day or so and chaulk it up to them being very busy. If you still can not get a hold of them, then i would suggest you take your business elsewhere and find a new and reputable tuner.
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Old 02-17-19, 08:42 AM   #3
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Default Re: Cold start stumble after 20 seconds

Well, that's good news that it's likely a tuning issue. That's what I'm hoping. Interested to know what table/parameter was adjusted to get this fixed. I found another shop who's willing to 'fix the issue' but, it sounds like I have to start the tune 100% back from scratch, and it would be a remote tune, so, that's like lighting a match to the money and time I just spent on this tune to begin with.


Yeah, I'm not real impressed with how they are handling it either. It's been over 1 month since the tune. I've sent 3 emails, left 1 voice mail, and talked to an actual guy who was going to 'talk to the tuner and get back to me'. Still...nothing. I actually drove to another state to go see these guys as they were supposedly some of the best around. Happy with everything else, just wish they'd give their customers 5 minutes of their time and at least make an effort to get in touch. I'm going to have to call them back tomorrow and just keep trying until I get ahold of someone I guess.
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Old 02-19-19, 08:57 PM   #4
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Default Re: Cold start stumble after 20 seconds

I always have that stumble whenever I reset the ECU, but only on 2nd start up after the ECU reset.

I saw on my datalog and i think is to do with short term fuel trim learning, as if i recall it will go very lean for a few seconds and then it settles. The subsequent start up won't have this stumble.

But I remembered during the tuning (e-tune), that stumble will always be there whenever i start the car (cold start especially) and i mentioned to my tuner about it and adjustment was made to correct it.

Last edited by dlheman; 02-19-19 at 09:00 PM.
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Old 02-20-19, 10:17 PM   #5
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Default Re: Cold start stumble after 20 seconds

Definitely tuning related. I had this as well, tuner revised his tune to fix it.
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Old 02-21-19, 08:26 AM   #6
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Default Re: Cold start stumble after 20 seconds

its your Cranking injector tables. The tuner needs to scale it better. IE add more fuel based on temps.
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Old 02-28-19, 09:10 AM   #7
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Default Re: Cold start stumble after 20 seconds

After about 30+ days of waiting for a revision from my tuner, I finally received one yesterday. The problem is better, but still not resolved. It still stumbles and wants to die, but it's not nearly as harsh as it was. I'm hoping they can resolve this completely here soon.

It was explained to me by them, that for some reason the O2 sensor isn't fully warmed up yet, and the car expects it to be, and then tries to compensate for an overly rich condition, which isn't there.

He said he "adjusted the closed loop delay a bit for this revision to give the front o2 more time to warm up and to allow the post start enrichment table to run a bit longer before entering closed loop mode.".

I'll try to keep this thread updated in the event we get the issue resolved to help others who may encounter this problem moving forward.
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Old 03-06-19, 05:57 AM   #8
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Default Re: Cold start stumble after 20 seconds

Does anyone know if the maps on an AP are locked? I know the AP itself is married, but what I'm not sure about is the maps.

By that I mean, can I find a different tuner to edit the map my current tuner made and adjust them and see if they can help resolve this issue? Emailed my tuner another log and more information last week, and still haven't heard anything back at all. After dealing with this issue for like 40+ days now since the tune, I think it's safe to say they're not really interested in helping.

** edit - finally got ahold of my tuner, and they want to see the car back. Supposedly, they're scheduling something up next week. Hopefully they follow through, and we can put this issue to bed.

Last edited by haive_music; 03-20-19 at 06:40 AM.
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Old 03-06-19, 07:25 AM   #9
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Default Re: Cold start stumble after 20 seconds

They’re locked if the tuner locked them, which most of them do.
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Old 03-22-19, 01:18 AM   #10
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Default Re: Cold start stumble after 20 seconds

that happened to me after my first tune....took 4 attempts. No tune is perfect out the door. Will have its minor flaws and needs to be driven to find the minor kinks. Though some has came out flawlessly..
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