2002 Subaru Wagon

Engine Performance problem
2002 Subaru Wagon 4 cyl All Wheel Drive Automatic 85000 miles

replaced gas filter no service lights on dash, car runs kinda ok till it warms up ahten bucks surges stalls, felt like plugged gas filter changed that out, slightly better but still stalls and surges, when you shut it off for a while it seems to recover again till it warms up, also added 1 can carb/injector cleaner and one bottle heet dry gas, been 4 hours and still no diff, HELP!
hylndr@ptd. Net farsix@hotmail. Com
March 18, 2009.

Hi: It may be a fuel problem. Have you checked fuel pump pressure? Also, have you checked closely for vacuum leaks? This is the 2.5L correct?

Says upstream oxy sensor is not acting correctly not dead not shorted but something

I agree fuel is acting on and off, thats why I tryed the fuel filter first, service at subaru says fuel air mixture sensor which may be the O2 sensor could be the culprit, there was lots of back pressure in the fuel line to the injector when I did the filter, how much I'm not sure, but it sprayed back against my thumb 4 a bit seemed pretty good. Oh at 80mph and above it seems to steady out and run smooth, so fuel obviously can get to the engine in quantity at some times, gotta be something acting on the pcm it would seem, I was going to try to blow air under pressure back thru the fuel line to see if there was any obstruction but that doesnt seem to be the case now.

Thing is the o2 sensor has been giving a mil on and off for a year or so, we just run it hot for an hour or so and the light would go out for a few days or a week damn thing iis 180 bux, doesnt the pcm just go to a default less efficient setting when this happens? It never did this surging bucking starviing for fuel action before, like I said I added methyl alcohol to absorb any water and auto zone sold her a can of gas treatment to work thru the injector. Any thing else you can think of?

Mar 19, 2009.
Chances are it is the O2 sensor. Before doing that, however, I think it would be a good idea to check engine compression. The 2.5L have a problem with blowing head gaskets. I'm starting to wonder if you have a problem there (bank 1) and it is causing the O2 sensor to go crazy.

As far as your question regarding the computer defalting to a less efficient setting, you would think so. That is why I'm starting to question the headgasket.

You are the best. If not you will sure do till he gets here, lol the headgasket was just replaced under warranty 6 weeks ago, since then we have noticed a burning smell occasionally like rubber or grease, took it back in and the dealer said it was nothing just some oil spilled on a manifold now this, ok they need to check the head gasket again is the o2 sensor on both heads or just one? Do you know which dids its on? I'm not sure which head they pulled, or is the sensor in the exhaust just before the cat converter? The pic in the book looks like its in the head or exhaust manifold below the valve cover everything is so freekin tight you need little jap hands to touch anything let alone get a wrench on it, sheesh, thanks so much you are helping a lot, Dave

Mar 19, 2009.