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Old 02-05-2021, 02:01 PM   #1
Blakeyohn
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Default P0171 - Replace intake gaskets?

About a month ago, my 2011 WRX threw CEL code P0171 (System too lean). Only real symptom was a very rough idle that only happened after restarting the car after filling up at a gas station. Brought it to the dealership and they replaced the engine filter, serviced the MAF sensor, and unclogged a vent hose in the gas tank for the rough idle.

Now it's a few weeks later and the CEL is back. This time they want to replace the intake gaskets and say it requires pulling the engine to do so, approx $1500! I havent been able to find much online about the intake gaskets or how much they should cost to replace. Not sure if I just bite the bullet on this one. I'm kind of worried about paying the cost for this and then discovering something else is causing the CEL.

Btw, the car is totally stock aside from an axleback.
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Old 02-05-2021, 09:58 PM   #2
DrD
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2012 Legacy 2.5GT
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Well - it sort of sounds like they are just guessing... if it's the intake gaskets, they should be able to smoke the intake and find the leak - no leak means the gaskets are fine. (the repair procedure has you check the exhaust to make sure it's leak-tight, then check the intake to make sure it's leak tight, then start looking at fuel pressure, coolant temperature, MAF sensor, etc.)

if the intake manifold gaskets are really leaking, then they can be replaced - the engine does not need to come out (based on the service manual) though it does look like it takes a bit to get the manifold out to replace the gaskets (might not have to do everything in the manual to get there, though)
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Old 02-06-2021, 12:43 PM   #3
CaptainSlowbaru
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Location: Rafferty Subaru, PA
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2002 Outback Sport
Green

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Look around the base of the upper plenum, see if it looks wet with oil. If it is, those gaskets are leaking. I've replaced many for this leak. THE ENGINE DOES NOT COME OUT. Don't go to that dealer- they don't know what they're doing!

I recently did this same job on an '09 Legacy GT. Once the manifold is off, there's more to the job: Breather hoses get hard as a rock and split, turbo inlet tube (if there's any oil on it, it will swell where it connects to the turbo) PCV valve assembly and hoses(the PCV valve is threaded into a plastic housing which always breaks when replacing the valve, and the hose coming out the top of the block will probably split when removing the valve assembly).

Where in NJ are you?
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Old 02-09-2021, 10:55 PM   #4
AliBenn
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Miles?

One thing on this list of causes not addressed
Front O2


https://www.engine-codes.com/p0171_subaru.html

As far as intake leaks go
Easy way is to spray chlorinated brake cleaner (bad stuff)
Over intake gaskets while car idling
If engine stumbles or revs there is your leak
GL
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Old 02-14-2021, 05:30 PM   #5
Jubbsta
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Hey, as AliBenn stated spraying brake clean around you intake system will show where there is a leak - when the engine sucks in the brake clean (which is combustible) it'll throw off your stoichiometric ratio and cause the engine to sputter as if it were about to stall. Though I don't usually recommend using chlorinated brake clean as the fumes can be pretty dangerous. Often I see the intake gaskets, tumble generator valve gaskets, and a small rubber cap on the passenger side of the intake manifold to be leaking. Do keep in mind, sometimes these gaskets will only leak when the engine is cold - if you can't replicate a system lean code - you can't properly diagnose it. Most common causes - failing intake system, fuel pressure issue, faulty MAF sensor, faulty coolant temp sensor, exhaust leak BEFORE the o2 sensors (not after). If you have a scan tool that can read live data I can send you a test plan as to what you should be looking for. Goodluck!
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Old 02-24-2021, 01:03 PM   #6
Jp925
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Could you pleas share what things should be reading? I have this issue on a freshly rebuilt 07 STi and I have rom raider to view live values.

Quote:
Originally Posted by Jubbsta View Post
Hey, as AliBenn stated spraying brake clean around you intake system will show where there is a leak - when the engine sucks in the brake clean (which is combustible) it'll throw off your stoichiometric ratio and cause the engine to sputter as if it were about to stall. Though I don't usually recommend using chlorinated brake clean as the fumes can be pretty dangerous. Often I see the intake gaskets, tumble generator valve gaskets, and a small rubber cap on the passenger side of the intake manifold to be leaking. Do keep in mind, sometimes these gaskets will only leak when the engine is cold - if you can't replicate a system lean code - you can't properly diagnose it. Most common causes - failing intake system, fuel pressure issue, faulty MAF sensor, faulty coolant temp sensor, exhaust leak BEFORE the o2 sensors (not after). If you have a scan tool that can read live data I can send you a test plan as to what you should be looking for. Goodluck!
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Old 02-26-2021, 02:52 PM   #7
Jp925
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Solved my issue, swapped a MAF with another STi and sure enough the p0171 popped up on the other car. Car leaned out in higher gears usually around 60mph, bought a Denso for a smooth 120 and all is good.
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Old 02-26-2021, 08:11 PM   #8
Vancouver98STi
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1998 JDM Impreza STi
V4 GF8 White

Question

Quote:
Originally Posted by DrD View Post

Well - it sort of sounds like they are just guessing...
Quote:
Originally Posted by CaptainSlowbaru View Post

Don't go to that dealer- they don't know what they're doing!
Makes you wonder if these "mechanics" are crooks... or just totally incompetent.
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Old 03-31-2021, 10:02 AM   #9
424wrx
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You can do intake gaskets with just lifting the intake manifold some and a pick set and mirror. I did mine years ago on the 08 wrx i had. I didnt remove anything.
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