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Oxygen sensor questions?

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What would be symptoms of a failing o2 sensor?


Car seems to randomly lose power, almost stall, or stall, tach jumping around a bit searching, starts right away again after stalls, but will either run ok again/or like crap... Seams ok when engine is cold, but after warm up and driving for a while it will happen, often just when idleing at a light or something.


Ive changed the knock sensor and cleaned up the MAF and idle air control valve...


Now im thinkin could be o2?

Not throwing a code currently..


Any help would be greatly appreciated,

Thanks guys

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  • 2 weeks later...


ON the 1st Gen cars the O2 sensor doesn't do as much. If car is stalling/dying I'd replace the MAF (it may not set a CODE/cause the CEL to come on even if bad and cleaning won't fix it)...easy if your car is a '92+ as they all used the Green Label/plastic JECS/AUTECS MAFs, which are the same for ALL Subaru Legacy/Outback/GT/Forester/Impreza from thru '98 (some '99). If yours is the silver/metal from the '90-91 years, less common.


Hit up your local PullandSave or other wrecking yard - or post on here or Legacy Central and you should be able to get one for less than $40. If bought @ a yard you can usually return it if it doesn't fix the issue.



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My 93 had the silver MAF when I got it. The MAF was bad and it took me months to track down the problem and replaced it. I had hesitation problems and sputtering. It did force me to work everything over though. Fixed every boost leak (there were a lot), replaced the injectors, replaced the fuel pump with a Walbro, etc... It was maddening. When I replaced the MAF the car finally drove like I thought it should.
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