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2020 Acadia Denali Rough Idle and Check Engine Light (P030X)

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Amanda S. · rep 0 · May 22, 3:38 AM · 1 replies · solved · Question

Vehicle: 2020 GMC Acadia Denali

My 2020 GMC Acadia Denali, with the 3.6L V6 engine, has developed a really rough idle recently. It feels like the engine is shaking more than usual when I'm stopped at a light, and sometimes I can feel a slight hesitation when accelerating. The biggest concern is that the Check Engine Light came on, and when I had it scanned at an auto parts store, it showed codes like P0301 and P0303.

These codes indicate misfires on cylinders 1 and 3. I'm not sure if it's spark plugs, ignition coils, or something more serious. The vehicle has about 55,000 miles on it. Has anyone else experienced this with their Acadia, and what was the fix? I want to get this sorted out before it causes any damage.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:38 AM

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ClearTheCode admin answer:

Diagnostic Trouble Codes P0301 and P0303 indicate a misfire detected in cylinder 1 and cylinder 3, respectively. A rough idle and hesitation are classic symptoms of engine misfires. Here's a breakdown of common causes and steps:

Common Causes:

  1. Ignition System:
    • Spark Plugs: Worn or fouled spark plugs are a very common cause of misfires. They are a routine maintenance item.
    • Ignition Coils: A failing ignition coil for a specific cylinder will prevent the spark plug from firing correctly.
  2. Fuel System:
    • Fuel Injectors: Clogged or faulty fuel injectors can prevent enough fuel from reaching the cylinder.
    • Low Fuel Pressure: Issues with the fuel pump or fuel pressure regulator can lead to insufficient fuel delivery to all cylinders.
  3. Air/Vacuum Leaks:
    • Vacuum Leaks: Leaks in the intake manifold gasket, vacuum lines, or PCV system can introduce unmetered air, causing a lean condition and misfires.
  4. Engine Mechanical Issues: (Less common but possible)
    • Low Compression: Worn piston rings, valves, or head gasket issues can lead to low compression in a cylinder, causing a misfire.

What to do:

  1. Inspect Spark Plugs and Coils: Start by inspecting and potentially replacing the spark plugs and ignition coils for cylinders 1 and 3. It's often recommended to replace all spark plugs if they are due for maintenance.
  2. Check for Vacuum Leaks: A mechanic can perform a smoke test to identify any vacuum leaks in the intake system.
  3. Fuel System Diagnostics: Test fuel pressure and inspect fuel injectors for proper operation.
  4. Compression Test: If the above steps don't resolve the issue, a compression test can determine if there's an internal engine problem.

When to see a shop:

If replacing spark plugs and coils doesn't resolve the issue, or if you're uncomfortable performing these checks yourself, it's best to take your Acadia to a qualified mechanic. Driving with persistent misfires can lead to catalytic converter damage due to unburnt fuel entering the exhaust system, which is a very expensive repair.

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