2012 Subaru Impeza

Mike Owner/Technician Manteno, Illinois Posted   Latest  
2012 Subaru WRX 2.5L 5-spd—JF1GV7F6XCG025977
P0301 - Cylinder 1 Misfire Detected

Good morning we have this Subaru in from another shop at idle it will set p0301/p0302/p0303/p0304 and does seem to idle rough. Driving it runs fine the strange thing it shows plus 25 on the short term adaptive and 0 on the long term. if you raise the rpm it does not change. The previous shop did replace the coils and plugs with oem parts. I,m confused by the adaptives and why it does not flag a p0300 code any input would be appreciated. When we unplugged the mass air flow sensor the adaptives did appear to go into a more normal range so we did install a new one but still have the same readings .

Michael Mobile Technician
Clinton, Utah
Michael Default

Hi Mike, Just wondering if there is a vacuum leak? Check the intake manifold, Injector O-rings and for a stuck open EGR valve. (If it has EGR) If VVT, check to make sure the VVT system is working correctly.

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Maynard Technician
Elmira, Ontario
Maynard Default

It might be worth considering a skewed rear O2 sensor. Maybe unplug it and do a test drive etc.

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Randy Analyst
Denver, Colorado
Randy Default

Step 1: verify software. Do not skip this step. Step 2: Using a gas analyzer, measure lambda. If it's rich then check AF sensor if it is lean check for vacuum leaks, fuel quality etc. Step 3: Depends on the above results and then more data needed.

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Matthew Owner/Technician
Carlton, Oregon
Matthew Default

Is the Subaru going into closed loop? Just a thought but that might be why your adaptives aren't changing. Make sure it's actually getting up to temperature. I would second checking for a Biased O2/Lambda sensor.

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Hollis Technician
Boulder, Colorado
Hollis Default

I'll try and explain / answer your questions to the best of my ability. It's difficult to remotely diagnose these unless I can see, hear, smell, taste it. Some Freeze Frame Data would help. You stated, "if you raise the rpm it does not change" Test the A/F & O2 sensor's. See if FT's respond to snap throttle, artificial enrichment and a vac leak. You asked "Why it does not flag a…

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Alex Technician
Denver, Colorado
Alex Default

The STFT stays high with the RPMs raised. Note that manifold vacuum is still high (low) with RPMs raised in the service bay, so a vacuum leak is still a possibility. See if STFT improves on moderate acceleration while driving down the road. You might want to check fuel alcohol content. If it has a tank full of E-85, it will run lean. What are the A/F sensor readings at idle? Can you force the…

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Jonathan Technician
Tempe, Arizona
Jonathan Default

Has it got an aftermarket air intake "system" and filter?

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Mike Owner/Technician
Manteno, Illinois
Mike Resolution

Good morning finally got this one figured out we actually had two problems. First was the timing belt alignment marks were off. The vehicle had a service contract so they sent a adjuster to verify . After replacing the timing belt the vehicle seemed to run worse at idle which we also found a vacuum line had come off under the intake manifold. After replacing the timing belt and securing the…

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