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2018 Q50 3.0t Rough Idle and Misfire Codes (P0301, P0300)

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Heather Y. · rep 0 · May 22, 5:04 AM · 1 replies · solved · Question

Vehicle: 2018 Infiniti Q50 3.0t Luxe

Hey everyone, I'm hoping someone can help me out. My 2018 Infiniti Q50 3.0t Luxe has been acting up lately. For the past week or so, I've noticed a really rough idle, especially when I'm stopped at a light. The engine feels like it's shaking more than usual.

Yesterday, the check engine light came on, and the car felt like it had significantly less power, almost like it was struggling to accelerate. I managed to get it to an auto parts store and they pulled some codes, specifically P0301 (Cylinder 1 Misfire Detected) and P0300 (Random/Multiple Cylinder Misfire Detected).

I'm wondering what the most common culprits are for these issues on the VR30DDTT engine. I'm due for a spark plug change soon, but could it be something more serious like an ignition coil or even a fuel injector? Any advice on where to start troubleshooting would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:04 AM

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ClearTheCode admin answer:

It sounds like you're dealing with a classic misfire scenario, which the P0301 and P0300 codes confirm. The VR30DDTT engine in your 2018 Infiniti Q50 3.0t Luxe is a robust engine, but like any modern direct-injection twin-turbo setup, it has common points of failure that can lead to misfires.

Here are the most common causes and diagnostic steps:

  1. Spark Plugs: Given you're due for a change, this is the most likely culprit, especially for a specific cylinder misfire (P0301). Worn or fouled spark plugs can lead to incomplete combustion. Inspect the spark plug from cylinder 1 for excessive wear, carbon buildup, or oil fouling. It's generally recommended to replace all plugs at once.

  2. Ignition Coils: A failing ignition coil for cylinder 1 would directly cause a P0301. You can try swapping the ignition coil from cylinder 1 with a coil from a different cylinder (e.g., cylinder 3) and see if the misfire code follows the coil. If the code changes to P0303, you've found your faulty coil.

  3. Fuel Injectors: A clogged or failing fuel injector for cylinder 1 could also cause a misfire by not delivering enough fuel. This is less common than plugs or coils but still possible. Diagnostics for injectors often require specialized tools or a professional shop.

  4. Vacuum Leaks: A vacuum leak can cause a lean condition and lead to random misfires (P0300) or even specific cylinder misfires if the leak is localized. Inspect all vacuum lines and intake connections for cracks or loose fittings.

  5. PCV Valve: A faulty PCV (Positive Crankcase Ventilation) valve can sometimes lead to vacuum leaks or oil consumption, contributing to misfires.

When to see a shop:

If replacing spark plugs and swapping ignition coils doesn't resolve the issue, or if you're uncomfortable performing these diagnostics yourself, it's best to take your Q50 to a qualified mechanic. They have advanced diagnostic tools to test fuel pressure, injector function, and perform smoke tests for vacuum leaks, which can pinpoint the exact cause more efficiently and prevent further damage to your engine or catalytic converters from prolonged misfires.

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