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Rough Idle and Misfire on my 2018 Genesis G80 3.8L

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Chris P. · rep 0 · May 25, 4:35 AM · 1 replies · solved · Question

Vehicle: 2018 Genesis G80 3.8L

Hey everyone,

I've been experiencing a really rough idle in my 2018 Genesis G80 3.8L, especially when I'm stopped at a light. It feels like the engine is shaking more than it should, and sometimes I even notice a slight hesitation when accelerating from a stop.

Recently, the check engine light came on. I had it scanned, and it's showing multiple misfire codes, specifically P0301 (Cylinder 1 Misfire) and P0300 (Random/Multiple Cylinder Misfire Detected). The car has about 75,000 miles on it.

Has anyone else with a G80 3.8L experienced something similar? What was the fix? I'm hoping it's not something major, but the shaking is definitely concerning.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 4:35 AM

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ClearTheCode admin answer:

Experiencing a rough idle and misfires with P0301 and P0300 codes on your 2018 Genesis G80 3.8L at 75,000 miles is a common issue that can stem from several sources. Here’s a breakdown of potential causes and steps to diagnose:

  1. Spark Plugs and Ignition Coils:

    • Cause: Worn spark plugs or failing ignition coils are very common culprits for misfires, especially around your mileage. A failing coil can prevent a cylinder from firing correctly, leading to P0301 for Cylinder 1 and potentially P0300 if other cylinders are also struggling or affected by the overall engine imbalance.
    • Action: Inspect and replace spark plugs. If the issue persists or the misfire is isolated to one cylinder (P0301), swap the ignition coil from cylinder 1 to another cylinder and re-scan. If the misfire code follows the coil, replace the coil.

  2. Fuel System Issues:

    • Cause: Clogged fuel injectors can lead to an improper fuel-air mixture, causing misfires. A dirty fuel filter, though less common for specific cylinder misfires, can also impact overall fuel delivery.
    • Action: Consider a fuel system cleaner. If misfires persist, a professional might need to test fuel pressure and injector performance.

  3. Vacuum Leaks:

    • Cause: An unmetered air leak in the intake system can lean out the fuel mixture, causing rough idle and misfires. This often leads to P0300.
    • Action: Visually inspect vacuum lines, intake manifold gaskets, and PCV valve for cracks or disconnections. A smoke test can help pinpoint elusive leaks.

  4. Compression Issues:

    • Cause: Less common, but low compression in a cylinder due to worn piston rings or valve issues can cause a persistent misfire.
    • Action: This requires a compression test by a qualified technician.

When to See a Shop: If replacing spark plugs and checking basic ignition components doesn't resolve the issue, or if you're uncomfortable performing these diagnostics yourself, it's best to take your Genesis to a trusted mechanic or dealership. They have specialized diagnostic tools to accurately pinpoint the root cause, especially for fuel system or internal engine issues. Continued driving with a persistent misfire can damage the catalytic converter.

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