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2018 Infiniti Q50 3.0t Rough Idle and Misfire - CEL On

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Sarah K. · rep 0 · May 22, 5:02 AM · 1 replies · solved · Question

Vehicle: 2018 Infiniti Q50 3.0t LUXE

Hey everyone,

I'm having some trouble with my 2018 Infiniti Q50 3.0t LUXE and hoping someone here might have some insight. Lately, the car has developed a really rough idle, especially when I'm stopped at a light or in traffic. It feels like the engine is shaking more than it should.

On a few occasions, I've also felt a slight hesitation or stumble while accelerating gently, and the Check Engine Light (CEL) has come on. It usually stays on for a bit, then sometimes goes off, only to reappear later. I haven't noticed any significant loss of power, but the rough idle is definitely concerning.

Has anyone else experienced similar issues with their Q50, particularly the 3.0t engine? What did you find was the cause, and what was the fix? Any advice on where to start looking would be greatly appreciated before I take it to the dealership.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:02 AM

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ClearTheCode admin answer:

A rough idle accompanied by a misfire and a Check Engine Light (CEL) on your 2018 Infiniti Q50 3.0t LUXE often points to an issue within the ignition, fuel, or air intake systems. The 3.0t VR30DDTT engine is known for its performance but can exhibit these symptoms if certain components are failing or worn.

Common Causes & Diagnostics:

  1. Ignition System Issues:

    • Worn Spark Plugs: Over time, spark plugs degrade, leading to inefficient combustion and misfires. The VR30DDTT engine uses specific iridium plugs that have a recommended replacement interval.
    • Failing Ignition Coils: A faulty ignition coil can prevent a cylinder from firing correctly, causing a misfire. This is a very common cause of rough idle and CEL.
    • OBD-II Codes: You'll likely see codes like P0301, P0302, P0303, P0304, P0305, or P0306 (P030x indicates a misfire in cylinder 'x'). A general P0300 code means random/multiple cylinder misfire.

  2. Fuel System Problems:

    • Clogged Fuel Injectors: A dirty or failing fuel injector can deliver an incorrect fuel spray pattern or volume, leading to misfires.
    • Low Fuel Pressure: Issues with the high-pressure fuel pump (HPFP) or low-pressure fuel pump can starve the engine of fuel.

  3. Air Intake & Vacuum Leaks:

    • Vacuum Leaks: Unmetered air entering the engine due to a cracked hose or gasket can disrupt the air-fuel mixture, causing a rough idle.
    • Dirty Mass Air Flow (MAF) Sensor: A contaminated MAF sensor can send incorrect air readings to the ECU, affecting engine performance.

  4. Other Potential Causes:

    • PCV Valve: A failing PCV valve can cause vacuum leaks or oil consumption issues that lead to misfires.
    • Oxygen Sensors: Faulty O2 sensors can provide incorrect exhaust gas readings, leading the ECU to adjust the air-fuel mixture improperly.

When to See a Shop:

It's highly recommended to have your Infiniti Q50 inspected by a qualified mechanic or Infiniti dealership as soon as possible. While some basic checks (like visually inspecting spark plug wires if accessible) can be done, diagnosing misfires on a modern turbocharged engine like the VR30DDTT requires specialized tools and diagnostic equipment.

  • Professional Diagnosis: A shop can accurately read the specific misfire codes, perform cylinder balance tests, check fuel pressure, and conduct smoke tests for vacuum leaks.
  • Prevent Further Damage: Continuing to drive with a persistent misfire can lead to more severe issues, such as catalytic converter damage due to unburnt fuel entering the exhaust system.

Addressing this promptly will help maintain your vehicle's performance and prevent more costly repairs down the line.

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