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Rough idle and misfire codes on 2016 Accord EX-L

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Mike T. · rep 0 · May 25, 1:50 AM · 1 replies · solved · Question

Vehicle: 2016 Honda Accord EX-L 2.4L

Hi everyone,

I'm having some trouble with my 2016 Honda Accord EX-L, 2.4L with about 98,000 miles on it. Lately, it's developed a rough idle, especially when I'm stopped at a light. The check engine light came on, and when I scanned it, I got a P0301 code (Cylinder 1 Misfire Detected) and sometimes a P0300 (Random/Multiple Cylinder Misfire Detected).

I haven't changed the spark plugs since I bought it at 40k miles, so I'm wondering if that's the culprit. Could it be ignition coils too? What's the best way to diagnose this without just throwing parts at it? Any advice on spark plug brands or steps for DIY replacement would be great!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 1:50 AM

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ClearTheCode admin answer:

Experiencing a rough idle and misfire codes like P0301 and P0300 on your 2016 Honda Accord 2.4L at 98,000 miles strongly suggests an ignition system issue, with spark plugs being a primary suspect given your maintenance history.

Common Causes of Misfires (P030X codes):

  1. Worn Spark Plugs: Over time, the electrode wears down, increasing the gap and requiring more voltage to fire, leading to misfires. Honda typically recommends iridium plugs which last longer, but even these need replacement around 100k miles.
  2. Failing Ignition Coil: Each cylinder has its own ignition coil. A failing coil won't deliver enough spark to the plug.
  3. Fuel Injector Issues: A clogged or faulty fuel injector can cause a lean condition and misfire.
  4. Compression Issues: Less common, but low compression in a cylinder due to valve or piston ring issues can cause misfires.

DIY Diagnosis & Steps:

  1. Confirm Misfire Location: Since you have P0301 (Cylinder 1), you can swap the ignition coil from Cylinder 1 to another cylinder (e.g., Cylinder 2). Clear the codes. If the misfire moves to Cylinder 2 (P0302), then the coil is bad. If it stays on Cylinder 1, the issue is likely the spark plug or fuel injector for that cylinder.
  2. Spark Plug Replacement:
    • Tools: You'll need a spark plug socket (usually 14mm or 16mm, thin-walled), a ratchet, an extension, a torque wrench, and a gap tool (though pre-gapped iridium plugs are common).
    • Plugs: For your Accord, stick with OEM equivalent iridium spark plugs, such as NGK Laser Iridium or Denso Iridium Long Life. These are designed for your engine.
    • Procedure:
      1. Disconnect the negative battery terminal.
      2. Remove the engine cover.
      3. Disconnect the electrical connector from each ignition coil.
      4. Unbolt and remove each ignition coil.
      5. Using your spark plug socket and extension, carefully remove each spark plug. Inspect them for wear, oil fouling, or unusual deposits.
      6. Install the new spark plugs. Ensure they are correctly gapped (check your owner's manual, usually pre-gapped). Hand-thread them in first to avoid cross-threading, then torque to specification (typically 10-14 lb-ft for iridium plugs). Do not overtighten!
      7. Reinstall ignition coils and connectors.
      8. Reconnect the battery.
  3. Clear Codes: Use your OBD-II scanner to clear any remaining codes.

When to See a Shop:

  • If the misfire persists after replacing spark plugs and coils.
  • If you suspect a fuel injector issue (a professional can test injector flow and spray pattern).
  • If you suspect a compression problem (a compression test is needed).
  • If you're uncomfortable with the DIY steps, especially handling sensitive engine components or using a torque wrench correctly.
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