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2005 Forester X
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Discussion Starter · #1 ·
I have a 2005 forester X, completely stock engine. I threw a few codes awhile back that had to do, I thought, with the front O2 fuel mixture sensor. The codes were PO131 (O2 sensor circuit low voltage) and POO31 (HO2S heater control circuit low). The car was running just fine, but I was getting terrible fuel economy. I ordered a brand new front sensor, and I installed it a couple days ago and cleared the codes.

The codes stayed away for about a day, and then I got another CEL. Reader showed confirmed P1153 (no extra info), pending P2096 (Post catalyst fuel trim system too lean), and P0420 (Catalyst system efficiency below threshold). I have had the P0420 before, and I've read that its not a big deal, but I've never seen these other codes. At this point the car was running just fine still, but once again, the fuel economy was garbage.

Later the same day the codes came up, I went out to start my car. I live in a pretty cold environment (it was about -17C, 1.4F). The first time the car started up fine, but the idle dropped down right away and died. The second time the idle was surging, and barely staying alive. so the third time I blipped the trottle after it started and it idled fine. Then, as I was driving home, the engine has terrible power and would surge and stutter around 2000rpm. The car could barely hit highway speed, and could not climb hills without dropping at least one gear. The engine codes are still the same as before. Even after sitting in the garage for a night, the idle still surges.

Now I am at a loss and do not know what to do. I cleaned the MAF, and checked for vacuum leaks, as I read these are possible culprits.
Is my new sensor a dud?
Thanks in advance for the help!
 

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a maf sensor can go bad and cleaning wont fix it, it sounds as if it is running too lean, maf...... O2 sensors , ecu response, vacuum leak, intake gasket leak, throttle body leak or mis adjusted, or even head gasket leak , can do this, running lean,
 

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2005 Forester X
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57 Posts
Discussion Starter · #3 ·
Thanks for the suggestions and quick response Leland. The head gaskets and intake gaskets were replaced about a year ago, so I’m pretty sure they aren’t leaking. The wierd thing is, why did this all happen after I installed my new sensor? I reinstalled the old sensor and the car still has engine codes, but it runs ok. As soon as the new one is installed it starts running rough. I also checked the restistance of the heating element in both sensors. Old one was 2.7 ohms, new one was like 3.9 ohms. I was thinking of checking the connector where the sensor plugs in. Anybody know what kind of voltage should be there on all four pins?
Thanks!
 

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14 outback auto
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342 Posts
The op didn't tell us the mgf of the new O2 sensor. Maybe that would help. I had acceleration problems with my 02 but unfortunately I didnt have any codes. After changing a few other things, I replaced the front O2 sensor with a Bosch from Advanced Auto. Problem solved. For some parts, such as wires, quality for subaru is important. Maybe this is another case.
 

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^ I agree that it's very easy to get the wrong sensor even though it's supposed to work for a specific model; been there done that!
 

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2005 Forester X
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Discussion Starter · #6 ·
Update on a long dead thread.... I eventually swapped out the sensor for a different brand (denso I think) and voila, problem fixed. Returned the dud for a full refund. Thanks for all the help guys!
 
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