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2018 RX 350 Rough Idle and Check Engine Light - Misfire?

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Sarah K. · rep 0 · May 22, 4:42 AM · 1 replies · solved · Question

Vehicle: 2018 Lexus RX 350 F Sport

Hey everyone, hoping for some advice here. I have a 2018 Lexus RX 350 F Sport with about 75,000 miles on it, and lately, it's been acting a bit strange.

When I'm stopped at a light or in park, the engine feels like it's vibrating more than usual, and the idle is pretty rough. It's not constant, but definitely noticeable. A few times, it felt like it almost stalled, and then the Check Engine Light came on.

I haven't noticed any major power loss while driving, but the fuel economy seems to have dipped slightly. I'm wondering if this could be a misfire or something more serious. Has anyone experienced this with their RX 350? What should I be looking into?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:42 AM

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ClearTheCode admin answer: It sounds like your 2018 Lexus RX 350 F Sport is indeed experiencing symptoms consistent with an engine misfire or a related combustion issue. A rough idle, vibrations, and a Check Engine Light (CEL) are classic indicators.

Here are the most common causes for these symptoms in a Lexus RX 350:

  1. Worn Spark Plugs: After 75,000 miles, spark plugs can be nearing the end of their service life, leading to inefficient combustion.
  2. Faulty Ignition Coils: A failing ignition coil for one or more cylinders will prevent proper spark, causing a misfire.
  3. Clogged Fuel Injectors: If an injector isn't delivering the correct amount of fuel, the air-fuel mixture will be off, leading to a rough idle and misfire.
  4. Vacuum Leaks: Unmetered air entering the engine can disrupt the air-fuel ratio, causing a lean condition and rough running.
  5. Mass Airflow (MAF) Sensor Issues: A dirty or failing MAF sensor can send incorrect air intake readings to the ECU, leading to poor engine performance.
  6. Oxygen (O2) Sensor Malfunction: Faulty O2 sensors can cause the engine to run too rich or too lean, impacting idle quality and fuel economy.

Diagnostics: The first step is to get the OBD-II codes read. Common codes for these symptoms include:

  • P030x: (e.g., P0301, P0302, etc.) indicating a misfire in a specific cylinder. P0300 is a random/multiple cylinder misfire.
  • P0171/P0174: System too lean (Bank 1/Bank 2), often associated with vacuum leaks or fuel delivery issues.

When to See a Shop:

  • If the Check Engine Light is flashing, this indicates a severe misfire that could damage the catalytic converter. Drive as little as possible and get it to a shop immediately.
  • If you've checked the basic items like spark plugs and air filter and the issue persists, or if you're uncomfortable diagnosing further, a professional technician can perform more in-depth diagnostics, including fuel pressure tests, compression tests, and smoke tests for vacuum leaks. They have specialized tools to pinpoint the exact cause quickly and efficiently.
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