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2018 Q50 3.0t Rough Idle and Misfire Codes (P0301, P0303)

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Angela R. · rep 0 · May 22, 5:01 AM · 1 replies · solved · Question

Vehicle: 2018 Infiniti Q50 3.0t Luxe

Hey everyone,

My 2018 Infiniti Q50 3.0t Luxe has developed a really rough idle lately, especially when cold. The check engine light came on, and when I scanned it, I got P0301 and P0303, indicating misfires on cylinders 1 and 3.

I recently had the spark plugs replaced about 5,000 miles ago, so I'm hoping it's not that again. The car also feels a bit sluggish under acceleration. Any ideas on what could be causing this? Could it be ignition coils, or something else entirely?

Thanks for any help!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:01 AM

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ClearTheCode admin answer:

The P0301 and P0303 codes indicate misfires on cylinders 1 and 3. While spark plugs are a common cause, given they were recently replaced, we should look at other possibilities.

Here are the common causes and diagnostic steps:

  1. Ignition Coils: A failing ignition coil is a very common cause of misfires. Even if plugs were replaced, coils can fail independently. You can try swapping coils between a misfiring cylinder and a non-misfiring one to see if the code follows the coil.
  2. Fuel Injectors: Clogged or faulty fuel injectors can lead to an improper fuel-air mixture, causing misfires. A fuel system cleaner might help if it's a minor clog, but a failing injector will need replacement.
  3. Vacuum Leaks: A vacuum leak near the affected cylinders can lean out the mixture, causing misfires. Inspect vacuum lines and intake manifold gaskets for any cracks or loose connections.
  4. Compression Issues: Less common, but low compression in a cylinder due to valve issues or piston rings can cause misfires. This requires a compression test.
  5. Wiring Issues: Damaged wiring to the ignition coils or fuel injectors can also interrupt their operation.

When to see a shop:

If swapping coils doesn't isolate the issue, or if you're not comfortable performing these checks, it's best to take your Q50 to a qualified technician. They have specialized diagnostic tools to pinpoint the exact cause, such as injector pulse tests, fuel pressure tests, and compression tests, ensuring a correct and efficient repair.

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