The largest online repair guide library for every car

About us
Contact support
FAQ
Sign up
Sign in

Rough Idle and Misfires (P030x) on 2016 Lexus GS 350 - Spark Plugs?

0

Mike T. · rep 0 · May 25, 3:29 AM · 1 replies · solved · Question

Vehicle: 2016 Lexus GS 350 RWD

Hey guys,

My 2016 Lexus GS 350 (RWD) has started to develop a rough idle, and I'm occasionally feeling some hesitation or slight misfires when accelerating lightly. The check engine light came on, and my scanner pulled P0301 (Cylinder 1 Misfire) and P0300 (Random/Multiple Cylinder Misfire Detected). The car has about 78,000 miles on it.

Could this be as simple as needing new spark plugs? I know they're due around 60k-80k miles. Or should I be looking at ignition coils, fuel injectors, or something else entirely? Any specific things to check first for a 2016 GS 350? I'm comfortable doing some DIY diagnostics.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 3:29 AM

0

ClearTheCode admin answer:

It sounds like you're experiencing classic misfire symptoms on your 2016 Lexus GS 350, and at 78,000 miles, you're definitely in the ballpark for spark plug replacement. The P0301 (Cylinder 1 Misfire) and P0300 (Random/Multiple Misfire) codes confirm this is where you should focus your diagnostic efforts.

Here's a systematic approach to troubleshoot and resolve the issue:

  1. Spark Plugs (Most Likely Culprit):
    • Given your mileage, worn spark plugs are a very strong candidate. Lexus V6 engines typically use iridium-tipped plugs, which last longer but still wear out. Replacing all spark plugs (not just cylinder 1) is recommended. Use only OEM-specified Denso or NGK iridium plugs.
    • DIY Tip: When replacing, inspect the old plugs for fouling or unusual wear patterns, which can indicate other issues.
  2. Ignition Coils:
    • A failing ignition coil is another common cause of misfires. Since you have a P0301 for cylinder 1, you can try swapping the coil from cylinder 1 to another cylinder (e.g., cylinder 3). If the misfire code then moves to cylinder 3 (P0303), you've identified a faulty coil.
    • Inspection: Look for any cracks, carbon tracking, or corrosion on the coil boots and bodies.
  3. Fuel Injectors:
    • A clogged or failing fuel injector can also cause a misfire. This is less common than plugs or coils but is a possibility. You could try adding a high-quality fuel system cleaner to your tank, but for a specific cylinder misfire, a professional might need to test injector pulse or flow.
  4. Air/Fuel Delivery Issues:
    • Air Filter: A very dirty air filter can restrict airflow, leading to a lean condition and misfires. Check and replace if necessary.
    • MAF Sensor: A contaminated Mass Air Flow (MAF) sensor can send incorrect air readings to the ECU, affecting the air/fuel mixture. You can try carefully cleaning it with specialized MAF sensor cleaner (never use other solvents).
    • Vacuum Leaks: Inspect all vacuum lines and intake components for cracks or loose connections. A vacuum leak can introduce unmetered air, causing a lean condition and misfires.

When to See a Shop: If replacing the spark plugs and testing the ignition coils doesn't resolve the issue, or if you're uncomfortable with further diagnostics, it's time to visit a Lexus dealership or a trusted independent mechanic. They have advanced diagnostic equipment to perform compression tests, fuel pressure tests, and more in-depth analysis of the VVT-i system and fuel injectors to pinpoint the exact cause of the misfire.

Menu

Help & account