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Old 01-04-2019, 08:29 AM   #1
STIdreamn
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Default 20 second stumble on cold start 2018 STi

Hi all, trying to help a friend out. He has a 2018 sti that he purchased new. At about 5k miles he had the following mods installed by a reputable local tuner.
-dom3.5xtr, ID1050cc, AEM 320lph, aero FPR, iag rails and lines, cobb sf intake, perrin inlet, ets tmic, hks elh, cobb tbe. On pump 93.

Initially there was an issue post install of this cold start (sitting overnight) where it starts fine and idles for about 20 seconds nice and smooth, then stumbles bad for roughly 20sec until it smooths out again and will remain fine for the rest of the day. Even if it sits for 8hrs.

The boost controller was also loose flapping under the alternator cover and the outlet to the recirculating valve was crushed so his driveability was horribly considering there was little to no function of the recirc valve.

He brought it back to the original builder/tuner only to be told everything is fine and the stumble is normal, just hit the gas a little.

After talking him into bringing it to another shop, this time outside of RI, they found those issues and retuned the car to a safer level putting the fail safes and knock sensor back on.

The issue is still present. I tried taking a video which doesnt fully capture just how bad it shakes but you can get the idea. Like I said once it does it once it is fine starting the rest of the day.

https://youtu.be/IWTGKxBMxjM
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Old 01-04-2019, 10:15 AM   #2
Zcypot
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Mine did this this morning, it actually stalled. Barely started doing it when it got really cold, im running E85 though. Took 3 cranks to get it going, but I havent gotten the cold start revised yet.

I found out my BPV was staying open at idle, so thats the only thing I have fixed so far on the car.
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Old 01-04-2019, 11:51 AM   #3
viper_crazy
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Quote:
Originally Posted by Zcypot View Post
I found out my BPV was staying open at idle, so thats the only thing I have fixed so far on the car.
So you fixed it but did it fix the stumble?
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Old 01-04-2019, 02:39 PM   #4
Zcypot
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Originally Posted by viper_crazy View Post
So you fixed it but did it fix the stumble?
I dont think its related, but I will post what happens on my next cold start. I made it tighter during my lunch break, seemed like it was still cracking open on cold starts.
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Old 01-04-2019, 06:50 PM   #5
greygonzalez
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I have the same issue. Itís when the rear 02 sensor turns on and the fueling trims go nuts. It only takes a few seconds for it to properly adjust.

At the moment there is no fix from what I believe. I worked with a few tuners who told me this.
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Old 01-04-2019, 07:12 PM   #6
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Old 01-04-2019, 07:12 PM   #7
greygonzalez
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Does that sound the same? Attached video above
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Old 01-04-2019, 07:32 PM   #8
viper_crazy
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Quote:
Originally Posted by Zcypot View Post
I dont think its related, but I will post what happens on my next cold start. I made it tighter during my lunch break, seemed like it was still cracking open on cold starts.
I didn't think it would. Whether the BPV is open or not, the air that's being drawn in is still being metered by the MAF.
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Old 01-04-2019, 07:33 PM   #9
viper_crazy
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Quote:
Originally Posted by greygonzalez View Post
I have the same issue. Itís when the rear 02 sensor turns on and the fueling trims go nuts. It only takes a few seconds for it to properly adjust.

At the moment there is no fix from what I believe. I worked with a few tuners who told me this.
I wonder if these tuners have though to disable any rear O2 influence to see what happens. Cobb has a tech article on how to "delete rear O2" if it's the rear O2 that's causing issues.
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Old 01-04-2019, 11:46 PM   #10
STIdreamn
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Originally Posted by greygonzalez View Post
Hey man, I cant open it. Could you upload to YouTube?
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Old 01-05-2019, 01:09 AM   #11
kopele
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Can you log it? How are your long term fuel trims? It sounds like it's running rich, then it starts correcting it overcorrects and goes lean, and takes a while to find stoich.
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Old 01-05-2019, 06:31 AM   #12
greygonzalez
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Quote:
Originally Posted by STIdreamn View Post
Hey man, I cant open it. Could you upload to YouTube?


Sorry bro! I saw I didnít activate the shared link option. Try again. If not I will
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Old 01-05-2019, 09:17 AM   #13
STIdreamn
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Originally Posted by kopele View Post
Can you log it? How are your long term fuel trims? It sounds like it's running rich, then it starts correcting it overcorrects and goes lean, and takes a while to find stoich.
I'll have him try to log it. It's just like grey posted though were after about 10seconfs of being on it does it for a short time then it is fine for the rest of the day
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Old 01-07-2019, 05:40 PM   #14
Zcypot
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cold starts still dip for me, almost stall, ill have to talk to my tuner. Warms starts too. First 30-60secs I cant move the car or itll stall.
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Old 01-08-2019, 10:17 AM   #15
07wrxhaweye
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Quote:
Originally Posted by STIdreamn View Post
Hi all, trying to help a friend out. He has a 2018 sti that he purchased new. At about 5k miles he had the following mods installed by a reputable local tuner.
-dom3.5xtr, ID1050cc, AEM 320lph, aero FPR, iag rails and lines, cobb sf intake, perrin inlet, ets tmic, hks elh, cobb tbe. On pump 93.

Initially there was an issue post install of this cold start (sitting overnight) where it starts fine and idles for about 20 seconds nice and smooth, then stumbles bad for roughly 20sec until it smooths out again and will remain fine for the rest of the day. Even if it sits for 8hrs.

The boost controller was also loose flapping under the alternator cover and the outlet to the recirculating valve was crushed so his driveability was horribly considering there was little to no function of the recirc valve.

He brought it back to the original builder/tuner only to be told everything is fine and the stumble is normal, just hit the gas a little.

After talking him into bringing it to another shop, this time outside of RI, they found those issues and retuned the car to a safer level putting the fail safes and knock sensor back on.

The issue is still present. I tried taking a video which doesnt fully capture just how bad it shakes but you can get the idea. Like I said once it does it once it is fine starting the rest of the day.

https://youtu.be/IWTGKxBMxjM


If you guys are in Rhode Island i wouldnt take that car to anyone else but Matt Miner aka Subaru Jesus, I have never heard of him having any issue but if one did arrive post tune, he wouldn't stop fixing it until it was right. I don't have Facebook anymore but i know he is on a group called Masssubaru, look him up cuz i know he'll even try to figure out what's wrong with it now, even if he didn't do the first tune. Probably one of if not the best Subaru tuner in our area tbh.
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Old 01-08-2019, 06:16 PM   #16
STIdreamn
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Quote:
Originally Posted by Zcypot View Post
cold starts still dip for me, almost stall, ill have to talk to my tuner. Warms starts too. First 30-60secs I cant move the car or itll stall.
Yours must be different. His is only on first cold start of the day sometimes not every day it stumbles for a brief period.
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Old 01-09-2019, 10:15 AM   #17
Zcypot
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Quote:
Originally Posted by STIdreamn View Post
Yours must be different. His is only on first cold start of the day sometimes not every day it stumbles for a brief period.
odd idle

oh perhaps, well here is a vid of what mine does. Pretty much same thing on cold starts. Past couple mornings it hasnt happened though.
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Old 01-09-2019, 03:37 PM   #18
JSR84
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TGV Deletes can sometimes cause cold start issues, Mine would start and idle fine, but once the coolant temp hit a certain value and the enrichment lowered it would stumble a bit. I just kept the same warm up enrichment for one more cell and it solved it. Not the exact same situation, but perhaps somewhere to start.
It can be a hard issues to track down because it only happens in the particular situation.
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Old 01-10-2019, 07:12 AM   #19
STIdreamn
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Originally Posted by JSR84 View Post
TGV Deletes can sometimes cause cold start issues, Mine would start and idle fine, but once the coolant temp hit a certain value and the enrichment lowered it would stumble a bit. I just kept the same warm up enrichment for one more cell and it solved it. Not the exact same situation, but perhaps somewhere to start.
It can be a hard issues to track down because it only happens in the particular situation.
That could be a possibility as well. However he even had the car completely retuned by a very reputable tuner I recommended to him and still has this one bug.
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Old 01-10-2019, 10:47 PM   #20
Haive_Music
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Sounds like the issue I have with my 17. My issue happens exactly 20 seconds after the car starts (cold starts only), but the issue clears up after 2-3 seconds every time. Car goes really lean, and it shoves the RPM's up to compensate.

At first, I thought it was related to the TGV's, however, we did some logs, and the tune shows that the TGV ratio remains the same. My current tuner said it was related to me removing the air pump, but that doesn't make much sense to me, unless that's when the car would normally be turning the air pump off (if it were equipped), and when it does that, it would expect less air, and thus provide less fuel.

In either case, I would have expected my tuner to be knowledgeable of this, considering air pumps have been being removed for for how many years on these cars. After 3 revisions, even though the issue was getting better, it was still unresolved. I've since scheduled a tune with another tuner. I'm hopeful they will be able to fix this issue once and for all.
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Old 01-14-2019, 01:01 AM   #21
STIAH64
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Iím having the same issue from now 2 reputable tuners. Video link:

2018 STI

Block:
-OEM Block
-Closed Deck
-Pinned Mains
-Manley H Tuff Rods
-99.75 bore 8.5:1 Manley XD pistons
-King Subaru Bearings (main and rod)
-Killer B oil pickup and baffle
-Fluidampr Damper
-ECM Billet timing guide
-ARP Head Stud kit

Turbo:
-FP Black HTZ

Intercooler:
-PRL FMIC

Exhaust/Manifold:
-Killer B 4-1 EL headers wrapped
-Killer B Uppipe (vbanded)
-44 Tial EWG 17lb spring
-Dump tube
-Invidia (divorce plate) Catless DP
-R400 catback*

Intake:
-Cobb with box
-84mm turbo inlet
-Turbosmart BOV (in BPV config)

Fuel:
-DW 300c Pump
-Fuellab universal EFI regulator
-IAG Fuel Rails
-IAG Fuel line kit
-ID 1000 injectors (top feed)
-IAG TGV deletes

Sensors:
-Grimspeed 3 port boost controller
-Innovate Wideband
-Cobb fuel pressure sensor
-Cobb 4 Bar MAP Sensor
-Viscounti w/ IAT Hybrid MAF harness
-Electric oil temp and pressure

Other:
-IAG AOS competition
-Mishimoto Oil Cooler
-Air pump delete plates
-ACT XT-M perf Street Pringle clutch
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Old 01-14-2019, 10:40 AM   #22
Zcypot
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Join Date: Nov 2013
Chapter/Region: SCIC
Location: Compton, CA
Vehicle:
2014 WRX Sedan Lmtd
WRB

Default

Quote:
Originally Posted by STIAH64 View Post
Iím having the same issue from now 2 reputable tuners. Video link:
http://youtu.be/im_pzbEjw_Q

2018 STI

Block:
-OEM Block
-Closed Deck
-Pinned Mains
-Manley H Tuff Rods
-99.75 bore 8.5:1 Manley XD pistons
-King Subaru Bearings (main and rod)
-Killer B oil pickup and baffle
-Fluidampr Damper
-ECM Billet timing guide
-ARP Head Stud kit

Turbo:
-FP Black HTZ

Intercooler:
-PRL FMIC

Exhaust/Manifold:
-Killer B 4-1 EL headers wrapped
-Killer B Uppipe (vbanded)
-44 Tial EWG 17lb spring
-Dump tube
-Invidia (divorce plate) Catless DP
-R400 catback*

Intake:
-Cobb with box
-84mm turbo inlet
-Turbosmart BOV (in BPV config)

Fuel:
-DW 300c Pump
-Fuellab universal EFI regulator
-IAG Fuel Rails
-IAG Fuel line kit
-ID 1000 injectors (top feed)
-IAG TGV deletes

Sensors:
-Grimspeed 3 port boost controller
-Innovate Wideband
-Cobb fuel pressure sensor
-Cobb 4 Bar MAP Sensor
-Viscounti w/ IAT Hybrid MAF harness
-Electric oil temp and pressure

Other:
-IAG AOS competition
-Mishimoto Oil Cooler
-Air pump delete plates
-ACT XT-M perf Street Pringle clutch


yup thats what mine does, but dips a tiny bit more. Oddly enough it didnt dip this morning, and I KNOW my vacuum line is torn really bad right now, so I guess its not related.
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Old 01-14-2019, 10:45 AM   #23
STIAH64
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Quote:
Originally Posted by Zcypot View Post
yup thats what mine does, but dips a tiny bit more. Oddly enough it didnt dip this morning, and I KNOW my vacuum line is torn really bad right now, so I guess its not related.
Yea Iím in the same boat, everything and I mean everything has been gone through. It seems to be related to whatís accessible in the ECU tuning wise. Iíve been told twice by two different locations and dyno/pro tunes that this is a norm for a SD tune on the 18ís. I tell you what Iíll pay a premium to whomever can fix this without shutting off the cold start loop.

I took another video (quite a lot more stutter like your suggesting) and log. Going to be sending those out again to try and identify something.
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Old 01-14-2019, 11:24 AM   #24
Zcypot
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Join Date: Nov 2013
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Location: Compton, CA
Vehicle:
2014 WRX Sedan Lmtd
WRB

Default

Quote:
Originally Posted by STIAH64 View Post
Yea Iím in the same boat, everything and I mean everything has been gone through. It seems to be related to whatís accessible in the ECU tuning wise. Iíve been told twice by two different locations and dyno/pro tunes that this is a norm for a SD tune on the 18ís. I tell you what Iíll pay a premium to whomever can fix this without shutting off the cold start loop.

I took another video (quite a lot more stutter like your suggesting) and log. Going to be sending those out again to try and identify something.
oh are you tuned on Speed density as well?
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Old 01-14-2019, 11:27 AM   #25
STIAH64
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Quote:
Originally Posted by Zcypot View Post
oh are you tuned on Speed density as well?
Now I am yes, even when I was Hybrid I had the same exact issue. Iím not even on E, Pump 93 until I figure this issue out.
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