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2018 Genesis G80 3.8L Rough Idle and Misfire - CEL On

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Ashley M. · rep 0 · May 22, 6:16 AM · 1 replies · solved · Question

Vehicle: 2018 Genesis G80 3.8L Premium

Hey everyone,

I've been experiencing some issues with my 2018 Genesis G80 3.8L Premium lately. For the past week or so, the car has developed a noticeable rough idle, especially when cold. It feels like there's a slight vibration through the steering wheel and seat.

Yesterday, the check engine light came on, and the car felt a bit hesitant under light acceleration. It's not a constant thing, but definitely noticeable. I'm worried it might be something serious.

Has anyone else with a G80 experienced similar problems? What was the cause, and what did you do to fix it? Any advice on where to start looking would be greatly appreciated before I take it to the dealer.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 6:16 AM

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ClearTheCode admin answer:

It sounds like your 2018 Genesis G80 is experiencing a common issue related to engine misfires, which is consistent with a rough idle and a check engine light. The hesitation under acceleration further supports this diagnosis. When the CEL illuminates, it's crucial to retrieve the diagnostic trouble codes (DTCs) to pinpoint the problem.

Common Causes for Misfires (P030x codes):

  1. Ignition System:
    • Worn or fouled spark plugs.
    • Failing ignition coils (a very common culprit).
    • Damaged spark plug wires (less common on modern engines).
  2. Fuel System:
    • Clogged or faulty fuel injectors.
    • Low fuel pressure (faulty fuel pump or regulator).
    • Contaminated fuel.
  3. Air/Vacuum System:
    • Vacuum leaks (intake manifold gasket, PCV system).
    • Dirty or faulty Mass Air Flow (MAF) sensor.
    • Clogged air filter.
  4. Engine Mechanical:
    • Low compression in a cylinder (worn piston rings, valve issues).
    • Carbon buildup on intake valves (especially with GDI engines).

Recommended Steps:

  1. Retrieve OBD-II Codes: Use an OBD-II scanner to read the codes. You're likely to see a P030x code (e.g., P0301 for cylinder 1 misfire, P0300 for random/multiple misfire). This will tell you which cylinder(s) are affected.
  2. Inspect Spark Plugs and Coils: If a specific cylinder misfire code is present, swap the ignition coil from the problem cylinder to a known good cylinder. If the misfire follows the coil, you've found your culprit. Also, inspect the spark plugs for wear or fouling.
  3. Check for Vacuum Leaks: Listen for hissing sounds around the intake manifold and vacuum lines. A smoke test can definitively identify small leaks.
  4. Consider Fuel System Checks: If ignition components are ruled out, a shop can perform fuel pressure tests and inspect injector performance.

When to See a Shop:

  • If you don't have an OBD-II scanner or are uncomfortable performing basic diagnostics.
  • If swapping coils or replacing spark plugs doesn't resolve the issue.
  • If the misfire is persistent, severe, or accompanied by other symptoms like stalling or significant power loss.
  • If the codes indicate issues beyond simple ignition components (e.g., catalytic converter efficiency codes, or multiple random misfires that aren't easily traced to one component).

Driving with a persistent misfire can damage your catalytic converter due to unburnt fuel entering the exhaust, so addressing this promptly is important.

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