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Rough Idle After DIY Spark Plug Change - 2020 G70 3.3T

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Ryan M. · rep 0 · May 22, 6:22 AM · 1 replies · solved · Question

Vehicle: 2020 Genesis G70 3.3T

Hey everyone,

I recently decided to tackle a DIY spark plug replacement on my 2020 Genesis G70 3.3T. I followed a few online guides and thought I did everything correctly. The car started up fine, but now I'm experiencing a noticeable rough idle, especially when cold. It feels like it's misfiring occasionally, and the engine just doesn't sound as smooth as it used to.

I used the recommended OEM plugs and torqued them to spec. I'm worried I might have messed something up. Has anyone else experienced this after changing their plugs on a G70, or any Genesis for that matter? Could it be something simple I overlooked?

Any advice or troubleshooting steps would be greatly appreciated before I have to take it to the dealership. Thanks!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 6:22 AM

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ClearTheCode admin answer:

It's not uncommon to encounter issues after a DIY spark plug replacement, especially with modern engines that are sensitive to small discrepancies. Here are some steps you can take to diagnose and potentially resolve the rough idle on your 2020 Genesis G70 3.3T:

  1. Recheck Coil Pack Connections:

    • Ensure all ignition coil packs are fully seated and securely connected to their respective spark plugs. A loose connection can cause intermittent misfires.
    • Verify that the electrical connectors to each coil pack are firmly clicked into place.

  2. Inspect Spark Plugs and Gaps:

    • While you used OEM plugs, double-check that they are the correct part number for your specific engine. Incorrect heat range or design can cause issues.
    • Even pre-gapped plugs can sometimes be off. Verify the gap on each plug using a feeler gauge. An incorrect gap can lead to poor combustion.

  3. Check for Vacuum Leaks:

    • During the spark plug replacement, you likely removed intake components. Inspect all vacuum lines and intake manifold connections for any signs of dislodgement or damage. A vacuum leak can introduce unmetered air, causing a rough idle.
    • Listen for any hissing sounds around the intake manifold or vacuum lines with the engine running.

  4. Scan for Diagnostic Trouble Codes (DTCs):

    • If you have access to an OBD-II scanner, check for any stored codes. Misfire codes (e.g., P0301, P0302, P0303, etc., indicating a misfire in cylinder 1, 2, 3, respectively, or P0300 for random misfires) would pinpoint the problematic cylinder.
    • Other codes related to fuel trim or oxygen sensors could also indicate an underlying issue.

  5. Inspect for Damaged Wires/Connectors:

    • Carefully look for any pinched, cut, or damaged wires leading to the coil packs or injectors that might have occurred during the process.

When to See a Shop:

If after performing these checks, the rough idle persists, or if you're getting persistent misfire codes on multiple cylinders, it's best to consult a professional mechanic or a Genesis dealership. They have specialized diagnostic tools that can perform more in-depth tests, such as compression tests, fuel pressure tests, or oscilloscope readings of ignition signals, to accurately identify the root cause. Continuing to drive with a persistent misfire can potentially damage the catalytic converter over time.

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