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Rough Idle and Misfire on 2016 IS 200t - Spark Plugs?

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Sarah K. · rep 0 · May 22, 4:45 AM · 1 replies · solved · Question

Vehicle: 2016 Lexus IS 200t

Hey everyone,

I've got a 2016 Lexus IS 200t with about 85,000 miles on it. Recently, I've noticed a rough idle, especially when the engine is cold. The car also feels a bit sluggish under acceleration, and the check engine light came on. I pulled the codes with my OBD scanner, and I'm getting P0301, P0302, and P0300.

From what I understand, P0301 and P0302 are misfires on cylinders 1 and 2, and P0300 is a random/multiple misfire. Could this be due to worn spark plugs? I don't think they've ever been changed since I bought the car used at 40k miles.

What's the recommended spark plug replacement interval for the 2016 IS 200t? Is this a straightforward DIY job, or should I take it to a mechanic? Any specific plug recommendations?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:45 AM

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Hi Chris,

Your diagnosis of misfires (P0301, P0302, P0300) at 85,000 miles on your 2016 Lexus IS 200t strongly points towards worn spark plugs as a primary suspect. The 2.0L turbocharged engine in your IS 200t (8AR-FTS) typically uses iridium-tipped spark plugs, which have a longer service life, but they are not immortal.

Here's what you should consider:

  1. Spark Plug Interval: For the 8AR-FTS engine, Lexus generally recommends spark plug replacement around 60,000 to 80,000 miles. At 85,000 miles, your plugs are definitely due, and likely past their optimal performance.
  2. Recommended Plugs: Always use OEM (Original Equipment Manufacturer) equivalent iridium spark plugs. Denso or NGK are common OEM suppliers for Lexus. Using incorrect plugs can lead to performance issues or even engine damage.
  3. DIY Difficulty: Replacing spark plugs on the 8AR-FTS engine is a moderately difficult DIY job. It involves removing the engine cover, ignition coils, and potentially some other components to access all four plugs. Ensure you have the correct tools, including a torque wrench for proper installation, and anti-seize compound for the plug threads.

Causes of Misfires & When to See a Shop:

  • Worn Spark Plugs: The most common cause, as the electrode wears down, requiring more voltage to spark.
  • Faulty Ignition Coils: A failing coil pack can cause misfires on specific cylinders. You could swap coils between cylinders to see if the misfire code moves.
  • Fuel Injector Issues: Clogged or faulty fuel injectors can also lead to misfires.
  • Vacuum Leaks: Can cause a lean condition and rough idle.
  • Compression Issues: Less common but serious, indicating internal engine problems.

If replacing the spark plugs doesn't resolve the misfires, or if the check engine light returns with the same codes, it's crucial to have a professional Lexus technician diagnose the issue further. They can perform more in-depth tests on the ignition coils, fuel injectors, and engine compression.

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