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2020 QX50 Essential: Rough Idle and Misfire Codes (P0301, P0303)

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David L. · rep 0 · May 22, 5:04 AM · 1 replies · solved · Question

Vehicle: 2020 Infiniti QX50 Essential

Hey everyone,

My 2020 Infiniti QX50 Essential, with the VC-Turbo engine, has developed a really rough idle lately. It feels like the engine is shaking more than usual, and sometimes it even stumbles a bit when I'm stopped at a light. The Check Engine Light came on, and when I scanned it, I got P0301 and P0303, indicating misfires in cylinders 1 and 3.

I've only got about 60,000 miles on it, and I'm surprised to be having these issues already. Has anyone with a VC-Turbo QX50 experienced similar misfire problems? What was the cause and solution?

I'm hoping it's something relatively simple like spark plugs, but I'm open to any suggestions before I take it in. Thanks for your help!

✓ Accepted solution

ClearTheCode Admin

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

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ClearTheCode admin answer:

Misfire codes (P030x) indicate that the engine's computer has detected that a specific cylinder (or multiple cylinders) is not firing correctly. For your 2020 Infiniti QX50 with the VC-Turbo engine, this can be due to several factors related to the 'air, fuel, or spark' triangle.

Common Causes & Diagnostics:

  1. Spark Plugs: Worn or fouled spark plugs are a very common cause of misfires. Even at 60,000 miles, depending on driving conditions, they could be due for replacement or inspection.
    • Action: Inspect spark plugs for wear, carbon buildup, or damage. Replace if necessary, ensuring correct gap and type for the VC-Turbo engine.
  2. Ignition Coils: A failing ignition coil for a specific cylinder will prevent the spark plug from firing.
    • Action: You can often swap coils between misfiring and non-misfiring cylinders to see if the misfire code follows the coil. If it does, replace the faulty coil.
  3. Fuel Injectors: Clogged or faulty fuel injectors can lead to an improper fuel-air mixture, causing misfires.
    • Action: A fuel system cleaner might help with minor clogs. For more severe issues, a shop can test injector flow and spray patterns.
  4. Vacuum Leaks: Leaks in the intake manifold or vacuum lines can introduce unmetered air, leaning out the mixture and causing misfires, especially at idle.
  5. Variable Compression Mechanism Issues: The VC-Turbo engine's unique variable compression system is complex. While less common, issues with its actuators or sensors could potentially affect combustion.
  6. Low Compression: In more severe cases, low compression in a cylinder (due to valve issues, head gasket, or piston rings) can cause misfires. This is usually diagnosed with a compression test.

When to See a Shop:

  • If replacing spark plugs and swapping coils doesn't resolve the issue.
  • If you suspect fuel injector problems or vacuum leaks, as these often require specialized diagnostic tools.
  • If the misfire is severe, causing significant shaking or a flashing Check Engine Light (a flashing light indicates a severe misfire that can damage the catalytic converter).
  • Any issues related to the VC-Turbo's unique variable compression system should be handled by an Infiniti dealer or a specialist familiar with this engine.
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