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Rough Idle and Misfires on my 2020 WRX - CEL Flashing

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Chris P. · rep 0 · May 22, 3:14 AM · 1 replies · solved · Question

Vehicle: 2020 Subaru WRX Base

Hey everyone,

I'm having a serious problem with my 2020 Subaru WRX Base. The Check Engine Light (CEL) started flashing yesterday, and the car is running really rough, especially at idle. It feels like it's shaking, and there's a noticeable loss of power when I try to accelerate. I also smell a bit of raw fuel sometimes.

I pulled the codes with my OBD-II scanner, and I'm getting P0301 (Cylinder 1 Misfire Detected) and P0300 (Random/Multiple Cylinder Misfire Detected). This is really concerning for a car with only 45,000 miles on it. What could be causing this, and what should I check first?

I'm hoping it's something relatively simple like spark plugs, but I'm worried it could be something more serious. Any advice on troubleshooting this would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:14 AM

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ClearTheCode admin answer:

A flashing Check Engine Light (CEL) accompanied by P0301 and P0300 codes on your 2020 Subaru WRX indicates a severe misfire condition that needs immediate attention. A flashing CEL means the misfire is significant enough to potentially damage the catalytic converter due to unburnt fuel entering the exhaust. Here's a breakdown of common causes and steps:

  1. Common Causes for Misfires (P030X codes):

    • Ignition System:
      • Spark Plugs: Worn, fouled, or incorrectly gapped spark plugs are a very common cause. Given your mileage, it's a strong possibility.
      • Ignition Coils: A failing ignition coil for cylinder 1 (P0301) would directly cause this. You can often swap coils between cylinders to see if the misfire code follows the coil.
    • Fuel System:
      • Fuel Injector: A clogged or faulty fuel injector for cylinder 1 could be failing to deliver enough fuel, leading to a lean misfire.
      • Fuel Pressure: Low fuel pressure across the rail could cause multiple misfires.
    • Air/Vacuum Leaks: A vacuum leak near cylinder 1 could lean out the air-fuel mixture, causing a misfire.
    • Engine Mechanical Issues: (Less common at your mileage, but possible)
      • Low compression in cylinder 1 due to valve issues or piston ring wear.
      • Carbon buildup on intake valves (especially with direct injection engines like the FA20DIT in your WRX) can impede airflow.

  2. Diagnostic Steps:

    • Check Spark Plugs: Inspect the spark plug for cylinder 1. Look for fouling, wear, or damage. Consider replacing all plugs if they are due for service.
    • Test Ignition Coils: Swap the ignition coil from cylinder 1 with a known good cylinder (e.g., cylinder 3). If the P0301 code changes to P0303, you've found your faulty coil.
    • Inspect Fuel Injector: A mechanic can test the fuel injector's pulse and spray pattern. Sometimes, fuel injector cleaner can help, but a faulty one needs replacement.
    • Check for Vacuum Leaks: Listen for hissing sounds and visually inspect vacuum lines.

When to See a Shop:

Do not drive the car extensively with a flashing CEL. The unburnt fuel entering the exhaust system can quickly overheat and destroy your catalytic converter, which is a very expensive repair. You should have your WRX towed to a trusted mechanic or Subaru dealership immediately. They have specialized diagnostic tools to pinpoint the exact cause of the misfire efficiently and prevent further damage.

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