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john -aka eauto
john -aka eauto, ASE Certified Technician
Category: Subaru
Satisfied Customers: 16108
Experience:  15 years as a auto tech
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I have a 2013 subaru impreza wrx hatchback. It has 20000

Customer Question

Hi, I have a 2013 subaru impreza wrx hatchback. It has 20000 miles, and is stored during the winter. It lately seems to start idling a little rough if stuck in traffic or at a light. I did find a rodent nest in the airbox after storage last winter. I cleaned out the nest and replaced the air filter. Today in traffic, it idled a little rough and my check engine light came on. It runs great when driving. The codes are p0300b random multiple misfire (rough idle?) And p0451evap emission system pressure sensor/switch range/performance. One inconsistency is fuel. Sometimes our fuel contains 10 percent ethanol, but all Stewarts shops high octane is ethanol free. Dont know if this could cause any issue with idle or trigger a code. There is no rust underneath since it doesn't see salted roads at all. I am meticulous with maintenance, and my car is like new, so these issues are surprising to me. Only modification is a Cobb tuning cat back exhaust.. please help. Also, slight rough idle started after I found and cleaned out rodent nest from airbox.please help!
Submitted: 1 year ago.
Category: Subaru
Expert:  john -aka eauto replied 1 year ago.

the po 300 is a misfire code is it skipping? any damage to the coils or wireing to the coils?

Customer: replied 1 year ago.

its only inconsistent at idle sometimes. Like i said the car is like new, and i dont suspect any damage to any part of it. Ive had it since day one. I remember that it ran fine even with the rodent nest in the airbox and filter, but when i cleaned the airbox and replaced the air filter, when i started it up, it immediately threw a code related to the sensors around the airbox. i cleared them, and they never came back. I could inspect the coils and wiring, but dont expect to find any damage

Expert:  john -aka eauto replied 1 year ago.

po300 is generally a primary ignition and or coils are the generally the cause is it under warranty.. Stwearts? You must be from Ny or vt

Customer: replied 1 year ago.

thanks will have to get back to you

Expert:  john -aka eauto replied 1 year ago.



  • Detected when two consecutive driving cycles with fault occur.
  • Immediately at fault recognition (A misfire which could damage catalyst occurs.)
Expert:  john -aka eauto replied 1 year ago.

if you need further help let me know