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2017 Tacoma V6 rough idle and occasional misfire, especially cold

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Tom H. · rep 0 · May 22, 2:16 AM · 1 replies · solved · Question

Vehicle: 2017 Toyota Tacoma TRD Off-Road

My 2017 Toyota Tacoma V6 (3.5L) has developed a really rough idle, especially when I first start it up in the morning or after it's been sitting for a while. It feels like it's shaking more than usual, and sometimes I get a noticeable stumble or misfire. The Check Engine Light has come on a couple of times, but then it goes off after a day or so.

When the CEL was on, I managed to pull a P030X code (I think it was P0303 for cylinder 3, but I'm not 100% sure now). The truck still drives, but the power feels a bit down, and the fuel economy seems to have dipped slightly. I've got about 80,000 miles on it.

Any ideas what might be causing this intermittent misfire and rough idle? Could it be spark plugs, or something more serious?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 2:16 AM

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ClearTheCode admin answer:

A rough idle and intermittent misfire, especially when cold, on a 2017 Toyota Tacoma V6 (3.5L) with a P030X code (P0303 for cylinder 3) points directly to an issue affecting combustion in one or more cylinders. Here's a breakdown of common causes and diagnostic steps:

  1. Spark Plugs:

    • Cause: Worn, fouled, or incorrectly gapped spark plugs are a very common cause of misfires. At 80,000 miles, while not necessarily past their service interval for iridium plugs, they could be contributing.
    • Action: Inspect the spark plugs, especially in cylinder 3. Look for signs of wear, oil fouling, or carbon buildup.

  2. Ignition Coils:

    • Cause: Each spark plug has its own ignition coil. If a coil is failing, it won't deliver sufficient voltage to the spark plug, leading to a misfire. Intermittent failures are common as coils heat up or cool down.
    • Diagnostics: If you have a P0303 code, swapping the coil from cylinder 3 to another cylinder (e.g., cylinder 1) and seeing if the misfire code follows (e.g., P0301) can help diagnose a faulty coil.

  3. Fuel Injectors:

    • Cause: A clogged, dirty, or failing fuel injector in cylinder 3 would prevent proper fuel delivery, causing a misfire. This is more likely if the misfire is consistent.
    • Diagnostics: Fuel injector testing (flow rate, spray pattern) or resistance checks can be performed by a mechanic.

  4. Vacuum Leaks:

    • Cause: An unmetered air leak in the intake system can lean out the air/fuel mixture, leading to a rough idle and misfires, especially when the engine is cold and running in open loop.
    • Action: Inspect all vacuum lines, intake manifold gaskets, and PCV valve for cracks or leaks.

  5. Mass Air Flow (MAF) Sensor:

    • Cause: A dirty or failing MAF sensor can send incorrect air intake readings to the Engine Control Unit (ECU), leading to an improper air/fuel mixture and misfires.
    • Action: Clean the MAF sensor with specialized MAF cleaner. If the problem persists, replacement might be necessary.

When to See a Shop:

  • Promptly: While intermittent, misfires can damage the catalytic converter over time due to unburnt fuel entering the exhaust. If the CEL is flashing, it indicates a severe misfire that could be actively damaging the catalytic converter, and you should stop driving immediately. Even if it's not flashing, it's best to get it diagnosed soon to prevent further issues and restore optimal performance and fuel economy.
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