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Old 01-15-2013, 01:58 PM   #1
Mr_Happy
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Join Date: Jan 2013
Chapter/Region: Tri-State
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2005 STi
CGM

Default System Too Lean (P0171)

Hey guys, 2005 STI with stock engine/exhaust and almost 107k miles.

Details: Car threw a P0171 code after install of P/S pump and boost gauge. Checked all hoses (which are zip-tied) and they're all fine. Sprayed carb cleaner around the engine bay and watched STFT's and it was all fine. So no leaks, or at least obvious ones. Don't think there's any cuz the carb cleaner would have exposed it. Car even started dying on me while driving when I'd push the clutch in while braking and turning. Also, this problem only occurs at idle. While driving the car feels great.

So, unplugged the MAF (even though it read normal) and the car ran amazing, literally the best I've heard/seen the engine run. So I thought it was the MAF. Got a new one right from Subaru and the CEL came back. Same code, same STFTs at 25%. MAF still reads ~ 3 g/s which I've asked around and heard is normal. So, my next guess is primary 02 sensor. The scanner never gets below 1.19x and sometimes goes all the way up to 1.3xx and would mostly hover around 1.2xx. This I've heard is what is also getting me the lean code. I was told the reading for the primary 02 sensor should be close to 1.000 and hop back and forth between lean and rich at idle. Mine is clearly staying lean. So should I try a new primary 02 and see what happens?
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Old 01-15-2013, 02:28 PM   #2
SuperScubi
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Join Date: Dec 2009
Chapter/Region: NWIC
Location: Kirkland, WA
Vehicle:
2004 Aspen White STi
PIA Tune 347whp 327tq

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You have a boost leak
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Old 01-15-2013, 02:45 PM   #3
Mr_Happy
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No I dont. I already tested for that. Plus I boost fine. Furthermore, if it were an air leak of some sort then my car would have continued to stall/die on me after disconnecting the MAF
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Old 01-15-2013, 04:04 PM   #4
SuperScubi
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PIA Tune 347whp 327tq

Default

I had the same issue last week. Installed a fmic and one of the clamps didn't clamp down all the way. The coupler pop off the pipe and I had a huge boost leak. I had the same problems as you described. I discconected the maf and is fired up just fine. Like nothing was wrong.

Check your boost gauge and all the lines
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Old 01-15-2013, 05:45 PM   #5
Mr_Happy
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Would you trust a dealership to do a boost leak test?
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Old 01-15-2013, 09:54 PM   #6
SuperScubi
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PIA Tune 347whp 327tq

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Nope... I trust independent Subaru shops tho
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Old 01-16-2013, 12:17 AM   #7
Mr_Happy
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I don't have any of those around. R/T Tuning is nearest me and they're 2 hours away
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Old 01-16-2013, 07:24 PM   #8
riddler12599
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is your maf bad?
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Old 01-16-2013, 09:03 PM   #9
Mr_Happy
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Quote:
Originally Posted by riddler12599 View Post
is your maf bad?
Refer to OP
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Old 01-16-2013, 09:22 PM   #10
nmlittlebigman
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2015 WRX LTD
WRB

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Quote:
Originally Posted by SuperScubi View Post
You have a boost leak
^^^ +1 ^^^

OP go here: http://forums.nasioc.com/forums/show...st+leak+tester

build it and use it...then report back. Leaks are sometimes tricky to track down under vacuum but will literally "scream" at you when you pressurize the intake track. I only use 7 or 8 psi and soapy water in a spray bottle.
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Old 01-17-2013, 03:41 PM   #11
Mr_Happy
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I'm going with the sensor for now. I was told you go up through the wheel and there's a hole in the fender to swap the O2 out? The dealer wants $125 and 1.5 hours of labor. Car is an 05 STI. Any idea with that? I'm thinking of doing it myself with that cost. I don't think I have a jack though
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Old 01-17-2013, 05:47 PM   #12
curtisboes
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Location: Jacksonville Florida
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04 WRX (STI Swap)
WRB

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Its easy to do it yourself.

Go to napa and buy a O2 sensor socket (I think they are like $15)
Jack up the car with the factory jack in your trunk or borrow one
take the passenger front wheel off
disconnect the NEG cable on the batt
unplug the O2 sensor
remove the sensor
now back track and put it all back together

took me 5 min to do mine a week or 2 ago

HOWEVER, I would also suggest checking for a boost leak as well but if not, thats your choice

good luck if you decided to do it yourself!
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Old 01-18-2013, 09:01 PM   #13
thomasm55
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the o2 is located on the passenger side
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Old 01-19-2013, 02:05 AM   #14
dead_eye
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Quote:
Originally Posted by Mr_Happy View Post
I'm going with the sensor for now.
In for the lulz.

I really think you should follow the advice and check for a boost leak first. The carb cleaner method doesn't seem to work on these cars, thats why everyone makes a tool to do it http://forums.nasioc.com/forums/show...st+leak+tester

I recently got this code and the car is totally stock. Its intermittently leaking somewhere I just have to find it.

Last edited by dead_eye; 01-19-2013 at 02:12 AM.
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Old 01-22-2013, 12:00 PM   #15
Mr_Happy
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Well, I have an appointment at R/T Tuning in Philly coming up and I'll have them smoke test it while I'm there and ill use the new O2 sensor anyway cuz mine will likely **** out sooner or later. Then if the smoke test doesn't work then ill start looking at fuel pressure and delivery
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Old 02-01-2013, 08:11 PM   #16
Mr_Happy
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Hole in intake manifold
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Old 02-02-2013, 12:02 AM   #17
majik1
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Sry, didn't see your post...
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Old 02-02-2013, 12:12 AM   #18
Mr_Happy
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It's post #1... Read it
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