The largest online repair guide library for every car

About us
Contact support
FAQ
Sign up
Sign in

2020 IS 300 Rough Idle, Misfire, and P0300/P0302 Codes

0

Mike T. · rep 0 · May 25, 3:25 AM · 1 replies · solved · Question

Vehicle: 2020 Lexus IS 300 AWD

Hi everyone,

I'm having a frustrating issue with my 2020 Lexus IS 300 AWD. For the past few weeks, I've noticed a rough idle, especially when the engine is cold or at stop lights. It feels like a slight vibration through the steering wheel and seat.

Yesterday, the Check Engine Light came on, and I scanned it. I got codes P0300 (Random/Multiple Cylinder Misfire Detected) and P0302 (Cylinder 2 Misfire Detected). The car still drives, but it feels a bit sluggish sometimes, and the rough idle is definitely more pronounced now.

I've only got about 45,000 miles on it. What could be causing this? Has anyone else experienced these specific codes or symptoms on their IS 300? Any insights or common fixes would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 3:25 AM

0

ClearTheCode admin answer:

The P0300 and P0302 codes on your 2020 Lexus IS 300 indicate a misfire, specifically in cylinder 2 and potentially other cylinders. This is a common issue that can stem from several sources in modern direct-injection engines.

Common Causes:

  1. Ignition System Components:
    • Spark Plugs: Worn or fouled spark plugs are a very common cause of misfires. Even at 45,000 miles, they could be due for replacement or inspection, especially if the engine has been running rich or lean.
    • Ignition Coils: A failing ignition coil for cylinder 2 (or other cylinders) will prevent proper spark, leading to a misfire.
  2. Fuel System Issues:
    • Fuel Injectors: A clogged, dirty, or faulty fuel injector for cylinder 2 will not deliver the correct amount of fuel, causing a misfire. Carbon buildup on injector tips is common in direct injection engines.
    • Low Fuel Pressure: A failing fuel pump or clogged fuel filter could lead to insufficient fuel delivery to all cylinders, causing random misfires (P0300).
  3. Air/Vacuum Leaks: Unmetered air entering the engine can lean out the air-fuel mixture, leading to misfires. Check for cracked vacuum hoses or a faulty PCV valve.
  4. Compression Issues: Less common, but low compression in cylinder 2 due to worn piston rings, valves, or a head gasket issue would cause a misfire.
  5. Carbon Buildup: In direct-injection engines like those in the IS 300, carbon buildup on the intake valves can restrict airflow, leading to misfires, especially at idle. This typically occurs at higher mileage but can start earlier depending on driving habits and fuel quality.

When to See a Shop:

  • Immediately: Driving with a persistent misfire can cause damage to the catalytic converter due to unburnt fuel entering the exhaust.
  • As soon as possible: A diagnostic is needed to pinpoint the exact cause.

Recommended Steps:

  1. Swap Ignition Coil: A common diagnostic step is to swap the ignition coil from cylinder 2 to a different cylinder (e.g., cylinder 4). If the misfire code moves to the new cylinder (e.g., P0304), the coil is likely faulty.
  2. Inspect Spark Plugs: Remove and inspect the spark plug from cylinder 2 and potentially other cylinders. Look for signs of wear, fouling, or damage.
  3. Fuel Injector Test: A shop can perform tests on the fuel injectors to check their spray pattern and flow rate.
  4. Vacuum Leak Check: A smoke test can help identify any vacuum leaks.
  5. Compression Test: If other diagnostics don't yield results, a compression test can rule out internal engine problems.
Menu

Help & account