97 OBW misfire - P0302

[JohnVT]

Hi -

just to ask for clarification? 97 OBW 130K miles. Just changed knock sensor (solved that code a couple of months ago), new NGK plugs, new wires, new ignition coil, new PCV valve, new fuel filter, new air filter.

Has been running rough again, about two months since all of that. Today, with a cold engine, headed immediately to the interstate, and got a flashing CEL, rough running, then steady. Code is P0302.

When I get home I'll check the plugs, wires again... Should I swap them around? Can the O2 sensor cause this, without throwing its own code?

What else should I look at?

 

THANKS.

[Cougar]

Hopefully this is due to a loose plugwire. You can swap plugs or wires if the problem persists and they will fit.

[unibrook]

My fix turned out to be the front 02 sensor. Here is my review from a diff thread: I have a 2001 Forester L with 85k miles on it. I have been chasing an intermittent hesitation under load problem for the past year. Only occurred when engine was warm. The front 02 sensor had been replaced once at 40k miles. I suspected it again this time, but since the only codes thrown had been cyl's 2&4 misfire ( p0302 & p0304) I assumed it must be ignition related. So I replaced plugs and wires 8 months ago...no effect. Did the dollar bill test over exhaust pipe, it was fine. Misted the coil, no sparks. I mentally sort of ruled out the fuel filter since it only happened when the engine was warm. Finally, a week ago while cruising on hwy at 65 mph, I felt the hesitation again (I wasn't even accelerating this time) and a new code was thrown....p0172. AutoZone read it for me, I described the symptoms to the guy and asked if he thought it might be the front 02 sensor. He said, "absolutely." So I decided to replace it next. Cost me $100.75 incl tax for the oem part# 22791aa00a from Cityside Subaru. I asked the Parts guy there if his experience was that this model engine needed a new front 02 sensor every 40k miles. He said, "no, these sensors are good for 100k miles." Well, bullsnot on that. I replaced the new front 02 sensor in 1 hour reaching from the top over the passenger side of the engine using an adjustable wrench. Be sure to use the thread lube so you can get it out easily next time.....after another 40k miles. I took out the air channel assembly first for better access. That seems to be the fix. No further hesitation since. Car runs like new.