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Discussion Starter · #1 ·
I have read extensively about the p0171 and p0174 lean codes. I could not find anything related to both codes being thrown at the same time. Both codes are currently being thrown, poor gas mileage and overheating on extended inclines.

Any ideas?
 

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Could be lots of things.
Let's start with basics: Year and model of your car with engine type. Any work done recently to the car?
 

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I have read extensively about the p071 and p074 lean codes. I could not find anything related to both codes being thrown at the same time. Both codes are currently being thrown, poor gas mileage and overheating on extended inclines.

Any ideas?
I think you need some more digits there. P1234

and what year, make, model, engine, transmission are you typing of, (I can fix the thread title).... I presume it is a subaru. newer then 1995.
 

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Discussion Starter · #4 ·
Sorry. That would help.

p0171 and p0174

2006 Outback with H6 engine 5EAT tranny.

I don't know what hasn't been done to this car. We inherited about a year ago from my father. I have stacks of paper work. Engine and tranny have been replaced after mutiple head gasket issues. Plus a ton of other smaller things.

But nothing has been done to the car recent to the codes showing.
 

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Sorry. That would help.

p0171 and p0174

2006 Outback with H6 engine 5EAT tranny.

I don't know what hasn't been done to this car. We inherited about a year ago from my father. I have stacks of paper work. Engine and tranny have been replaced after mutiple head gasket issues. Plus a ton of other smaller things.

But nothing has been done to the car recent to the codes showing.
fixed thread title.

front o2 sensor changed ?

radiator changed? if so with what, does it have a OEM thermostat and OEM rad cap? ($40 for that pair solve many a overheating problem.).

how many miles?
 

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Discussion Starter · #6 ·
fixed thread title.

front o2 sensor changed ?

radiator changed? if so with what, does it have a OEM thermostat and OEM rad cap? ($40 for that pair solve many a overheating problem.).

how many miles?
Thanks.

Radiator has been replaced.

Not sure if the front 02 sensor has been changed. Not sure about the thermostat and it does have an OEM cap.

188,000 on car, about 70,000 on engine

The car is fine around town. No overheating in traffic or elsewhere. Only on fairly long ascents does the car start to increase in temp.
 

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Thanks.

Radiator has been replaced.

Not sure if the front 02 sensor has been changed. Not sure about the thermostat and it does have an OEM cap.

188,000 on car, about 70,000 on engine

The car is fine around town. No overheating in traffic or elsewhere. Only on fairly long ascents does the car start to increase in temp.
your code condition "might" make the engine run lean, ... and running lean makes for more heat.

front o2 sensor makes that kind of code, and a few other things like MAP / MAF being dirty. but the o2 is kind of a cheap / easy fix, and they do wear/ age and get dirty , especially in cars that have engine problems. ($50-100 buys a denso branded one off rockauto or amazon....local parts stores like to rip the customer off for such things).

you might get some subsequent codes like a mild p0420, or minor misfires if things progress and you don't get a fix to the p0171/p0174.

are you running 91-93 octane?
 

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Discussion Starter · #8 ·
I should mention I cleaned MAF at air intake. It does have a K&N type of air filter and no housing.

I checked for vacuum leaks with carb cleaner and could not identify any.
 

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Discussion Starter · #9 ·
your code condition "might" make the engine run lean, ... and running lean makes for more heat.

front o2 sensor makes that kind of code, and a few other things like MAP / MAF being dirty. but the o2 is kind of a cheap / easy fix, and they do wear/ age and get dirty , especially in cars that have engine problems. ($50-100 buys a denso branded one off rockauto or amazon....local parts stores like to rip the customer off for such things).

you might get some subsequent codes like a mild p0420, or minor misfires if things progress and you don't get a fix to the p0171/p0174.

are you running 91-93 octane?
Only run premium. I did put a can of Seafoam in it last night.
 

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Only run premium. I did put a can of Seafoam in it last night.
chuck the K and N filter if its a wet type, and put on a OEM or similar paper filter. (some people here have done that on used subarus they have bought).

I watched a mechanic swap 318 in a dodge.
the only reason he could see, = starved for air on a consistent basis as the wet filter never gets clean. (impossible to remove the fine dust ).

_____

seafoam is great at fixing minor problems like gummy intakes on small engines, ....the best gas stablizer I ever used in can gas.

but I doubt you are going to get enough benefit out of it to fix the present issues.
 

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Discussion Starter · #11 ·
chuck the K and N filter if its a wet type, and put on a OEM or similar paper filter. (some people here have done that on used subarus they have bought).

I watched a mechanic swap 318 in a dodge.
the only reason he could see, = starved for air on a consistent basis as the wet filter never gets clean. (impossible to remove the fine dust ).

_____

seafoam is great at fixing minor problems like gummy intakes on small engines, ....the best gas stablizer I ever used in can gas.

but I doubt you are going to get enough benefit out of it to fix the present issues.
It is a CAI type so I imagine it is a wet filter. My only thought is it had the CAI long before the codes showed up.

I love seafoam in my motorcycles so I thought I would give it a shot.
 

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It is a CAI type so I imagine it is a wet filter. My only thought is it had the CAI long before the codes showed up.

I love seafoam in my motorcycles so I thought I would give it a shot.
subaru's oem is actually a good cold air intake with a snorkel, can't get any better (...although the companies that sell them want your money)


Cold air inductor ? got a pic of that? maybe its going terminal after a long long time.

the original K and N type needed rinsing and re-oiling on a consistent basis. ...and saturate with fluid.

some of the later ones were dry ones that you would rinse with water and dry (but still like getting 100% of the dust off impossible).

(my generator actually has a wet foam filter, I just rinsed and oiled it,...glad I don't run it in a dusty area...all grass and pavement).
 

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Discussion Starter · #13 ·
Yup, Cold air intake. I don't have a picture but I do have a new clean filter I can put in. Once my wife gets home I will put it in and see if it makes a difference.

I have 3 motorcycles that all take oiled air filters. You get a system down and they aren't too bad but they are no fun either.
 

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Discussion Starter · #14 ·
I just put in the new filter. No change.

The car idles fine but if I give a fair amount of gas in neutral the revs actually dip a bit and them come back up. Almost to the point of stalling. That would seem like a vacuum leak to me.
 

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Check carefully the intake tract from the MAF housing all the way to the throttle body. Any leaks will cause lean codes.

With a can of brake cleaner, spray around the base of the intake manifold into the heads, see if the RPMs drop. If so, you've found your leak.

Also, ditch the K and N system. The MAF sensor likes to absorb the oil reside from the filter, oiled properly or not.

I wouldn't be too surprised if there was an issue with the AVCS solenoids, possibly (getting lazy or stuck). If you have access to data logging equipment (RomRaider or similar), you can verify AVCS activity in real-time.
 

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Discussion Starter · #17 ·
Thanks for the info.

Eagle Eye the link to the codes was especially useful. I pulled the codes through the car and pulled up 2 more codes relating to the MAF. I replaced the MAF and that fixed all of the problems I was having! Thanks!!!
 
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