Impreza Outback / 99 / 110,000 mi / manual / everything stock
First the car started jerking (due to misfire I guess) when accelerating, especially pronounced at the at low RPMs of 2-nd and 3-rd gear. Nothing weird on idle or rev-ing the engine without load. No lack of power when it goes above 3000 RPM on the highway etc. In a couple of days I almost learned how to accelerate carefully with a bit more gas after each shift so you almost can't feel it.
Then the CEL turned on. Checked the code - P1130 - "Front oxygen sensor circuit malfunction (open circuit)". Reset the error code and in a while the generic P0302 - "Cylinder 2 Misfire Detected" appeared (no P1130 though).
Searched the web and found a couple of postings where this combination of symptoms - misfire/P1130 was due to bad fuel pump. Tried to compare which one is harder - to change the pump or the sensor and the sensor behind all those rusty bolts and under the car looked the worse one.
So changed the fuel pump and fuel filter. And nothing changed. Well may be the jerking a little bit and with the new pump the CEL never came off (guess some better fuel flow helped a bit).
Next thing, changed the O2 sensor. The store had the universal (and cheaper) one in stock. Read the warnings about the universal sensors but this was BOSCH and looked OK. The problem with it was that it had three wires while the OEM had four. The booklet has a conversion table and they claim the missing wire is the common so OK I'll buy that.
With the new sensor though I immediately get P1133 - "HO2S insufficient switching" and whenever I turn it off with the scanner it comes again in a couple of seconds. The misfire is much worse.
Any ideas? I know I messed up with the new sensor (as if the old one was good) not sure how though. There is a slight chance the new sensor was bad but this -http://glasairproject.com/soobdocs/codediag/P1133.gif talks only about bad connections. And I'm only 90% sure I connected it properly.
Running out of ideas... Except taking it to the dealer or buyng OEM sensor or even putting the old one back (which I still suspect is the faulty element). Or even worse - putting the old one back and going to the dealer so they can cure the original symptoms.
Any help is highly appreciated...
Not too long ago, I'd say "swap out the plug wires and see if it helps." Had a 94 mazda that had uneven acceleration and rough idling when it was damp outside...seemed to happen every 40,000 miles and every time a new set of plug wires fixed the problem. It was weird.
Anyway, that got me to thinkin... have Subies gone over the coil on plug or whatever the trend is to eliminating the need for high voltage plug wires in modern engines? If so, when?
Best Regards, -- Todd H. 2001 Legacy Outback Wagon, 2.5L H-4 Chicago, Illinois USA
Did you change the front O2 sensor? or the one downstream from the cat converter? If everything was stock as you said, that's about the mileage I'd expect afront O2 sensor to start being 'lazy' or going bad. Dosen't mean there aren't other problems too. a bad MAF can cause hesitation even stalling. I'd bet the fuel pump was fine. And plugs and wires wouldn't be a bad idea. Surely the plugs aren't original - if so they need changing! a good sorce for slightly cheaper OEM parts is www.subarugenuineparts.com . Think about putting an OEM sensor in the front O2 spot and changing plug wires. Often, misting the wires with a spray bottle of water at night sometimes will show sparking or cause misfiring if you want to try diagnosing the wires. Sometimes they carbon inside though. Subaru throttle body cleaner will somewtimes clean off the MAF element - if you have to change that guy for new its $$$$.
Replace the O2 sensor. If it hasn't gone already (which I think is what you have) it will soon anyway.
There are dozens of posts about this in the archives for this group alone, and I had the exact same instance of error and problems and it was just the sensor.
Thanks to everyone who responded! It was the spark plug wires. Changed the O2 sensor before that and it didn't fix it. Thanks for your help...