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Rough Idle and Misfire on my 2018 RX 350 F Sport

0

Ryan M. · rep 0 · May 22, 4:42 AM · 1 replies · solved · Question

Vehicle: 2018 Lexus RX 350 F Sport

Hey everyone,

I've been experiencing a really rough idle lately with my 2018 Lexus RX 350 F Sport. It feels like the engine is shaking more than usual, especially when I'm stopped at a light. Sometimes, it even feels like it's about to stall, though it hasn't actually died yet.

I also noticed a slight hesitation during acceleration, and the check engine light came on a few days ago. I got it scanned, and it's showing multiple misfire codes, specifically P0301 and P0303. Has anyone else with a similar model year RX 350 run into this? What was the fix?

I'm hoping it's something simple like spark plugs, but I'm worried it could be something more serious. Any advice or shared experiences would be greatly appreciated before I take it to the dealer.

✓ Accepted solution

ClearTheCode Admin

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

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Hello Sarah,

Rough idle and misfire codes (P0301, P0303, etc.) on a Lexus RX 350 can stem from several common issues. Here's a breakdown of potential causes and steps:

Common Causes:

  1. Worn Spark Plugs: Over time, spark plugs degrade, leading to inefficient combustion and misfires. This is a very common cause, especially if they haven't been replaced according to the maintenance schedule.
  2. Faulty Ignition Coils: Each cylinder has an ignition coil. If a coil fails, it won't provide adequate spark, causing a misfire in that specific cylinder (e.g., P0301 for cylinder 1).
  3. Clogged Fuel Injectors: A dirty or clogged fuel injector can prevent the correct amount of fuel from reaching the cylinder, leading to a lean condition and misfire.
  4. Vacuum Leaks: Unmetered air entering the engine through a cracked hose or gasket can disrupt the air-fuel mixture, causing rough idling and misfires.
  5. Mass Air Flow (MAF) Sensor: A dirty or failing MAF sensor can send incorrect air intake readings to the engine control unit (ECU), leading to an improper air-fuel ratio and subsequent misfires.

When to See a Shop:

  1. Immediate Action: If the check engine light is flashing, this indicates a severe misfire that could be damaging your catalytic converter. Drive as little as possible and get it inspected immediately.
  2. Professional Diagnosis: While spark plugs and coils can be DIY for some, diagnosing the exact cause of a misfire often requires specialized tools to check fuel pressure, injector pulse, and vacuum integrity. A professional shop can accurately pinpoint the problem.
  3. Persistent Codes: If the codes return after clearing, or if the rough idle persists despite basic checks, it's time for a professional diagnosis. They can perform a compression test or leak-down test if internal engine issues are suspected.
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