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Rough Idle & Misfire on 2020 GV80 3.5T - Spark Plugs?

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Mike T. · rep 0 · May 25, 4:38 AM · 1 replies · solved · Question

Vehicle: 2020 Genesis GV80 3.5T

Hey guys,

I'm experiencing a bit of a headache with my 2020 Genesis GV80 3.5T. It has about 55,000 miles on it. For the past week or so, I've noticed a rough idle, especially when the engine is cold. It feels like a slight tremor through the car. The check engine light also came on a couple of days ago.

I ran an OBD scan, and it's throwing a P030X code (P0302 specifically, for cylinder 2 misfire). My first thought is spark plugs, as I haven't changed them yet. What's the recommended interval for spark plug replacement on the 3.5T engine? Is this a straightforward DIY job, or are there any tricky parts I should be aware of? I've done plugs on other cars before, but never on a Genesis V6 turbo.

Any tips or shared experiences would be great!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 4:38 AM

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ClearTheCode admin answer:

A rough idle and a P0302 code (Cylinder 2 Misfire Detected) strongly suggest an ignition system issue, and spark plugs are a very common culprit, especially around your mileage.

  1. Recommended Interval: For the Genesis 3.5T engine, spark plug replacement is generally recommended every 45,000 to 60,000 miles. At 55,000 miles, you're right in the sweet spot for a replacement.
  2. Causes of Misfire (P0302):
    • Worn Spark Plug: The most common cause. Electrodes wear down, increasing the gap and requiring more voltage to spark, leading to misfires.
    • Faulty Ignition Coil: The coil for cylinder 2 could be failing, not delivering enough voltage to the plug.
    • Bad Fuel Injector: A clogged or failing injector for cylinder 2 can cause a lean or rich condition, leading to misfire.
    • Compression Issues: Less common, but low compression in cylinder 2 would also cause a misfire.
  3. DIY Considerations: Replacing spark plugs on the 3.5T engine is generally considered a moderate DIY task. Key points:
    • Access: The rear bank of cylinders can be a bit tighter to access than the front, requiring some patience and potentially different extension lengths.
    • Tools: You'll need a spark plug socket (typically 16mm or 5/8 inch), various extensions, a torque wrench for proper tightening, and dielectric grease for the coil boots.
    • Coil Packs: Be gentle when disconnecting and removing the ignition coil packs. Inspect them for any cracks or signs of damage.
    • Gap: Always double-check the gap on new spark plugs, even if they're pre-gapped, using a wire-type feeler gauge. Use OEM-specified plugs (e.g., NGK or Denso iridium).
  4. Troubleshooting Steps:
    • Since you have a P0302, you could swap the ignition coil from cylinder 2 to another cylinder (e.g., cylinder 4). If the misfire code moves to P0304, then the coil is bad. If it stays P0302, then the plug or injector is more likely.
    • If replacing the plugs doesn't resolve the issue, you'll need to investigate the coil pack and potentially the fuel injector for cylinder 2.
  5. When to See a Shop: If replacing the spark plugs and testing the coil pack doesn't clear the misfire, or if you're uncomfortable with the DIY process, a professional diagnosis is recommended. Continued misfires can damage the catalytic converter.
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