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Old 01-09-2018, 11:37 PM   #1
c4lvinnn
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Default Roughness/Misfire Cylinder 1 on Cold Start P0301

Have been looking at multiple threads and researching. Havent been able to pinpoint what the issue is.

Symptoms:
- AP registering Roughness Cylinder 1 between 8-35 on cold start idle. This usually starts to register when the cold idle RPMs start to dip down. All other cylinders register 0, at max 1 roughness. All misfires/roughness goes away once at operating temp
- CEL came on twice; I cleared ECU, however the code had been tripped and stored 3-4 times now WITHOUT CEL (and cleared code for that too) for the last 700 miles or so and tripped P0301 code for cyl 1 misfire
- Not sure if related but 2 wires on MAF harness have been repaired by PO. Sometimes chugs/lugs the car like dying MAF. Can resolve by jiggling the wiring and it comes back alive like normal.

I have tried the following without resolve:
- Cleaned MAF and IAT twice
- New OEM spark plugs all the way around
- New coil pack on cylinder 1
- Compression test: 135, 140, 135, 140 (motor was sitting for about 2.5hrs so it was pretty cold)
- Unplugged MAF at idle. CEL came on for MAF but no P0301 or roughness registering. Not sure if fluke or if it was kind of warmed up already
- Fuel system/injector cleaner run through a tank
- Not bad gas, only have had the car a few weeks and have gotten top tier gas only
- Reflashed a few times to both Stage 1 and Stage 1 + SF

Mods:
- Stage 1 + SF OTS Map
- Cobb SF Intake

Next I want to try a new MAF and if that doesn't resolve it, probably just not worry about it until I get a protune and have the shop diagnose it if its not some phantom misfire. And if it turns out its the MAF I may just go SD while I'm at it. Could it be injector? Vaccuum leak?

The car drives absolutely fine whether cold or warmed up and I can kind of feel the misses at idle, but its so slight you'd just shrug it off for being a boxer engine. Any ideas?
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Last edited by c4lvinnn; 01-10-2018 at 09:49 AM.
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Old 01-10-2018, 11:48 AM   #2
Subie_
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I recommend moving the injector to another cylinder to see if the misfire follows before replacing the MAF.

The ECU will compensate for a vacuum leak by adjusting your short term fuel trim (A/F Learned 1). Generally speaking, any adjustment exceeding ~ +/- 8% indicates a leak, or your MAF scaling is simply off. You can easily view this parameter real-time on Accessport, but I doubt this is the source of your issue because only one cylinder is affected. It would be a good idea to clean up the MAF harness while you're in there poking around.

It's not abnormal to see a pending code but no CEL, especially when you're aware of an underlying issue. The ECU is evaluating and poised to throw a CEL, but not all of the conditions to trigger it have been satisfied.
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Old 01-10-2018, 11:58 AM   #3
c4lvinnn
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Quote:
Originally Posted by Subie_ View Post
I recommend moving the injector to another cylinder to see if the misfire follows before replacing the MAF.

The ECU will compensate for a vacuum leak by adjusting your short term fuel trim (A/F Learned 1). Generally speaking, any adjustment exceeding ~ +/- 8% indicates a leak, or your MAF scaling is simply off. You can easily view this parameter real-time on Accessport, but I doubt this is the source of your issue because only one cylinder is affected. It would be a good idea to clean up the MAF harness while you're in there poking around.

It's not abnormal to see a pending code but no CEL, especially when you're aware of an underlying issue. The ECU is evaluating and poised to throw a CEL, but not all of the conditions to trigger it have been satisfied.
Thanks! Injector is on the list as well. I'm just not sure why it would go away (maybe rarely very low roughness at operating temp). Thats odd. And yes I wanted to try to cut the MAF harness right before where PO made repairs so I can re-crimp and re-pin the terminals on a new connector but I'm having the hardest time finding a replacement even on flea-bay.
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Old 01-10-2018, 12:18 PM   #4
viper_crazy
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What year and model do you have?
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Old 01-10-2018, 12:19 PM   #5
c4lvinnn
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Quote:
Originally Posted by viper_crazy View Post
What year and model do you have?
2011 STI
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Old 01-11-2018, 08:02 AM   #6
viper_crazy
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May not be what I'm thinking of, then, as I believe Subaru updated the part by that year, and usually the symptoms are a lot worse than what you're describing. I'll suggest what was on my mind though.

I have a 08 WRX and on cold mornings on a cold start it would run physically run rough, to the point of stalling sometimes and would have if I didn't keep my foot on the throttle. After it warmed up to a certain point, the problem went away. A bit of research turned up the culprit.

The rubber seals that seal the intake to TGV's were redesigned to be thicker in later years so it created a better seal during cold months. Replaced and never had an issue again.

That being said, I have a "plastic" intake. I'm not sure if you have a metal one or not, and if so, I'm not sure if that intake to TGV space is sealed the same way or not. I have a feeling this isn't your problem, but thought I'd mention it anyways. Maybe there's enough of a leak that may be causing the problem.
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Old 01-11-2018, 10:48 AM   #7
c4lvinnn
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Quote:
Originally Posted by viper_crazy View Post
May not be what I'm thinking of, then, as I believe Subaru updated the part by that year, and usually the symptoms are a lot worse than what you're describing. I'll suggest what was on my mind though.

I have a 08 WRX and on cold mornings on a cold start it would run physically run rough, to the point of stalling sometimes and would have if I didn't keep my foot on the throttle. After it warmed up to a certain point, the problem went away. A bit of research turned up the culprit.

The rubber seals that seal the intake to TGV's were redesigned to be thicker in later years so it created a better seal during cold months. Replaced and never had an issue again.

That being said, I have a "plastic" intake. I'm not sure if you have a metal one or not, and if so, I'm not sure if that intake to TGV space is sealed the same way or not. I have a feeling this isn't your problem, but thought I'd mention it anyways. Maybe there's enough of a leak that may be causing the problem.
Thanks. I may take a peek at it since things will be off when I do the AOS install (not looking forward to that...)

FYI P0301 code registered again this morning but no CEL. This time I'm NOT going to clear the code and see if it ends up turning CEL on.
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Old 01-11-2018, 12:04 PM   #8
Max Capacity
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I betting a 2011 has the newer orange O-rings.

You said you moved the wires the PO fix and the problem goes away...

"Not sure if related but 2 wires on MAF harness have been repaired by PO. Sometimes chugs/lugs the car like dying MAF. Can resolve by jiggling the wiring and it comes back alive like normal. "

Have someone who's good with a volt meter check that out.
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Old 01-11-2018, 12:56 PM   #9
c4lvinnn
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Originally Posted by Max Capacity View Post
I betting a 2011 has the newer orange O-rings.

You said you moved the wires the PO fix and the problem goes away...

"Not sure if related but 2 wires on MAF harness have been repaired by PO. Sometimes chugs/lugs the car like dying MAF. Can resolve by jiggling the wiring and it comes back alive like normal. "

Have someone who's good with a volt meter check that out.
No, it fixes the dying MAF/chugging/lugging issue that sometimes occurs. Separate issue from the P0301 misfire issue.
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Old 01-13-2018, 10:33 AM   #10
c4lvinnn
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So I left it overnight to sit and started it with an unplugged MAF. Let it idle for about 5 minutes. It did not register ANY roughness/misfires on any cylinders. It felt the same at idle so does anyone know if roughness monitoring through the AP is dependent on MAF connection? I'd hope not but you never know.
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Old 01-13-2018, 11:29 AM   #11
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No it isn't. I think it's obvious what your problem is though....
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Old 01-13-2018, 05:09 PM   #12
c4lvinnn
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So I unmarried the AP, put the stock intake back on and just drove more than 200 miles on the highway and back with no CEL coming back nor any P0301 registering a DTC on the ECU. I'll keep monitoring and driving, but looks like it may have been an OTS map issue. I do plan on getting a TBE soon anyway so I'm just going to get a protune then if this ends up being the issue. So odd...
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Old 01-13-2018, 05:18 PM   #13
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Which map version do you have for the SF intake? Just curious if there's been a revision or two. Sometimes the map may not download correctly or something with the map data became corrupt with moving and transferring.

It's worth a try. At the very least, try the regular stage 1 map (stock intake) and see what happens.
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Old 01-13-2018, 05:23 PM   #14
c4lvinnn
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Quote:
Originally Posted by viper_crazy View Post
Which map version do you have for the SF intake? Just curious if there's been a revision or two. Sometimes the map may not download correctly or something with the map data became corrupt with moving and transferring.

It's worth a try. At the very least, try the regular stage 1 map (stock intake) and see what happens.
It was stage 1 + sf v3.34 normal wg map. It was already part of the preloaded maps when I got the AP and the only one I moved over to it was a HWG stage 1 map just to test uploading maps to it. I did already try stock intake and stage 1 map. Same issue after a couple hundred miles it would register the code and throw CEL eventually. Maybe this car just hates OTS maps lol
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Old 01-13-2018, 05:34 PM   #15
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Maybe. Could be the OEM programming isn't as strict with its parameters. If you just flashed it, it may take a some miles to pop up again.

Some people (note, SOME people) have reported OTS maps to be better than OE maps, so maybe there is a legitimate problem and the OE map isn't reporting it.

Just possibilities, is all. I'd personally be keen to investigating why the difference.

Or it could be as you say. Your car doesn't want to change for you and accepts itself for who it is.
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Old 01-13-2018, 05:42 PM   #16
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Have the injectors been swapped yet?
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