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2017 Mirage G4 Rough Idle & Check Engine Light (P030X)

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Chris P. · rep 0 · May 22, 5:35 AM · 1 replies · solved · Question

Vehicle: 2017 Mitsubishi Mirage G4 ES

My 2017 Mitsubishi Mirage G4 ES, with about 70,000 miles, has started running really rough, especially at idle. The check engine light came on, and when I scanned it, I got a P0301 code, which points to a misfire in cylinder 1. Sometimes it feels like the whole car is shaking.

I'm thinking it might be time for new spark plugs, but I'm not sure if there's anything else I should check first. What's the recommended spark plug replacement interval for these cars? And what kind of spark plugs should I use? Is this something I can tackle myself, or should I take it to a mechanic right away?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:35 AM

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ClearTheCode admin answer:

A P0301 code on your 2017 Mitsubishi Mirage G4, indicating a misfire in cylinder 1, is a common issue that can often be resolved with routine maintenance. At 70,000 miles, spark plugs are a very strong candidate for the cause.

  1. Common Causes of P030X Misfire Codes:

    • Worn Spark Plugs: The most frequent cause. Over time, the electrode wears down, requiring more voltage to spark, leading to misfires.
    • Faulty Ignition Coil: The coil pack for cylinder 1 could be failing.
    • Clogged Fuel Injector: The injector for cylinder 1 might not be delivering enough fuel.
    • Vacuum Leak: Less common for a single cylinder misfire, but possible.
    • Low Compression: A more serious internal engine issue.

  2. Spark Plug Replacement Interval & Type:

    • Mitsubishi typically recommends replacing spark plugs on the Mirage G4 every 60,000 to 75,000 miles, so your vehicle is right in that window.
    • You must use iridium-tipped spark plugs. Mitsubishi engines are designed for these long-life, high-performance plugs. Using standard copper or platinum plugs can lead to poor performance, reduced fuel economy, and premature wear. NGK or Denso are common OEM suppliers.

  3. DIY Troubleshooting & Replacement Steps:

    • Confirm Misfire: Clear the code, then swap the ignition coil from cylinder 1 to another cylinder (e.g., cylinder 2). Drive the car until the check engine light returns. If the code changes to P0302, you've identified a bad coil. If it remains P0301, the issue is likely the spark plug or fuel injector.
    • Spark Plug Replacement:
      • Ensure the engine is cool.
      • Disconnect the negative battery terminal.
      • Remove the engine cover (if present).
      • Disconnect the electrical connector from the ignition coil for cylinder 1, then remove the coil.
      • Use a spark plug socket (typically 14mm or 16mm, thin-walled) with an extension and ratchet to remove the old spark plug.
      • Inspect the old plug for signs of wear, fouling, or damage.
      • Install the new iridium spark plug. Hand-tighten first, then torque to the manufacturer's specification (usually around 18-22 ft-lbs). Do not overtighten.
      • Reinstall the ignition coil and reconnect its electrical connector.
      • Repeat for other cylinders if you're doing a full set.
      • Reconnect the battery and clear any codes.

  4. When to See a Shop:

    • If swapping coils doesn't change the misfire cylinder, and new spark plugs don't resolve the issue.
    • If you're uncomfortable working with ignition components or don't have the proper tools (torque wrench, spark plug socket).
    • If you suspect a fuel injector issue or a more serious internal engine problem (e.g., if you hear unusual engine noises or see smoke).
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