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2017 IS 350 F Sport Rough Idle & Misfire Codes

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Mike T. · rep 0 · May 22, 4:38 AM · 1 replies · solved · Question

Vehicle: 2017 Lexus IS 350 F Sport

Hey everyone,

I'm having some trouble with my 2017 Lexus IS 350 F Sport, which has about 60,000 miles on it. Lately, it's developed a really rough idle, especially when cold, and sometimes feels like it's stumbling under light acceleration. The Check Engine Light came on, and my scanner pulled multiple misfire codes: P0300 (Random/Multiple Cylinder Misfire Detected), P0302 (Cylinder 2 Misfire Detected), and P0304 (Cylinder 4 Misfire Detected).

I've heard these 2GR-FSE engines can be sensitive. I'm wondering if it's spark plugs, ignition coils, or something more serious like fuel injectors. I replaced the spark plugs about 20,000 miles ago with OEM parts. Any ideas on the most likely culprit or what I should check first?

Thanks in advance for any help!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:38 AM

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ClearTheCode admin answer:

Multiple misfire codes (P0300, P0302, P0304) on your 2017 Lexus IS 350 F Sport indicate a problem with the combustion process in specific cylinders and potentially across the engine. Given the symptoms of rough idle and stumbling, this needs to be addressed promptly.

Here's a diagnostic approach:

  1. Ignition Coils: Even if spark plugs were recently replaced, an ignition coil can fail independently. Since you have specific cylinder misfires (2 and 4), a common diagnostic step is to swap the ignition coils from the misfiring cylinders with coils from non-misfiring cylinders (e.g., swap coil 2 with coil 1). If the misfire code follows the coil to the new cylinder, you've found the faulty coil.
  2. Spark Plugs: Although you replaced them 20k miles ago, a defective or fouled plug can still cause issues. Visually inspect the spark plugs from cylinders 2 and 4 for signs of fouling, damage, or incorrect gap.
  3. Fuel Injectors: Clogged or faulty fuel injectors can prevent adequate fuel delivery to a cylinder, leading to a misfire. This is a common issue, especially with direct injection engines. A fuel injector test (e.g., resistance check, spray pattern test) might be necessary.
  4. Compression Test: Low compression in a cylinder (due to valve issues, head gasket, or piston rings) will cause a misfire. This is a more serious mechanical issue and should be checked if other causes are ruled out.
  5. Vacuum Leaks: A vacuum leak can cause a lean condition and rough idle, potentially leading to misfires, especially if it's localized to certain cylinders or affects the overall air-fuel mixture.

When to See a Shop:

  • If swapping coils doesn't isolate the issue, or if you suspect fuel injector problems, a professional diagnosis is recommended. They have specialized tools to test fuel pressure, injector pulse, and perform more accurate compression tests.
  • If the misfires are severe, causing the car to shake violently or lose significant power, driving it extensively could damage the catalytic converter due to unburnt fuel entering the exhaust. Get it checked as soon as possible.
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