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2018 Q50 3.0t Red Sport - Rough Idle & Misfire, Time for New Plugs?

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Mike T. · rep 0 · May 24, 2:51 PM · 1 replies · solved · Question

Vehicle: 2018 Infiniti Q50 Red Sport 3.0t

Hey everyone,

I've got a 2018 Infiniti Q50 Red Sport with the 3.0t engine, currently sitting at about 65,000 miles. Lately, I've noticed a persistent rough idle, especially when the car is cold. It's not terrible, but definitely noticeable and a bit shaky.

More concerning, I've felt a slight hesitation under acceleration, and the engine just doesn't feel as strong as it used to. I haven't gotten a check engine light yet, but I'm worried it's coming. I'm thinking it might be time for new spark plugs, as I haven't changed them since I bought the car.

Is this a common issue for the VR30DDTT engine around this mileage? I'm pretty handy and have done basic maintenance before. Is changing the spark plugs on this engine a feasible DIY project, or should I just take it to a shop? Any tips or specific tools I might need would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 24, 2:51 PM

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ClearTheCode admin answer:

Your symptoms on a 2018 Infiniti Q50 3.0t Red Sport at 65,000 miles strongly suggest worn spark plugs, which is a common maintenance item for the VR30DDTT engine, especially if the car has been driven spiritedly or is tuned. While a Check Engine Light (CEL) with misfire codes (e.g., P0301-P0306) would confirm this, the rough idle and hesitation are clear indicators.

Causes & Diagnosis:

  1. Worn Spark Plugs: Over time, the electrode gap widens, requiring more voltage to fire, leading to misfires, especially under load or during cold starts. The VR30DDTT engine typically uses NGK DILKAR8A8 spark plugs, which are iridium-tipped and have a recommended replacement interval of 60,000 miles under normal conditions, or sooner if tuned.
  2. Ignition Coils: Less common but possible, a failing ignition coil could also cause similar symptoms. Often, this will trigger a specific misfire code for the affected cylinder.
  3. Fuel System: Clogged fuel injectors or a weak fuel pump could also contribute, though less likely to present solely as rough idle and hesitation without other symptoms.

DIY Spark Plug Replacement Steps (General for VR30DDTT):

  1. Gather Tools: You'll need a torque wrench, various extensions, a spark plug socket (typically 14mm thin wall), dielectric grease, anti-seize (optional, for threads), and a set of new spark plugs.
  2. Access: The VR30DDTT engine has coil packs directly on top of the spark plugs. You'll need to remove the engine cover, disconnect the electrical connectors from the coil packs, and unbolt/remove the coil packs.
  3. Remove Old Plugs: Use your spark plug socket and extension to carefully unscrew the old plugs. Inspect them for signs of oil fouling or abnormal wear.
  4. Install New Plugs: Apply a small amount of anti-seize to the threads of the new plugs (if desired, check plug manufacturer recommendations) and a dab of dielectric grease inside the coil pack boot. Hand-thread the new plugs to avoid cross-threading. Torque to manufacturer specifications (typically around 15-20 ft-lbs for these plugs). Do NOT overtighten.
  5. Reassemble: Reinstall the coil packs, connect the electrical connectors, and replace the engine cover.

When to See a Shop:

  • If you're uncomfortable working with engine components or don't have the proper tools.
  • If the issue persists after spark plug replacement, indicating a deeper problem like a failing ignition coil, fuel injector, or even a vacuum leak.
  • If you get a flashing Check Engine Light, which indicates a severe misfire that could damage the catalytic converter.
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