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2020 Acadia SLT Rough Idle and Stalling at Stops

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Emily N. · rep 0 · May 22, 3:41 AM · 1 replies · solved · Question

Vehicle: 2020 GMC Acadia SLT

Hello GMC forum,

I'm having an issue with my 2020 GMC Acadia SLT, 3.6L V6. Lately, it's developed a really rough idle, especially when I'm stopped at a light or in traffic. Sometimes it feels like it's going to stall, and it has actually stalled once or twice when coming to a complete stop.

There's no Check Engine Light on yet, which is frustrating because it makes it harder to diagnose. The car has about 45,000 miles on it. I've tried putting in premium fuel, but it hasn't made a difference. It feels like a misfire, but without a code, I'm at a loss.

Any ideas on what could be causing this? Could it be spark plugs already, or something else entirely?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:41 AM

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ClearTheCode admin answer:

It's certainly frustrating when you have driveability issues like a rough idle and stalling without a Check Engine Light (CEL). This often indicates an intermittent problem or one that hasn't yet met the parameters to trigger a diagnostic trouble code. For your 2020 GMC Acadia SLT 3.6L V6, here are some common culprits for these symptoms:

  1. Ignition System Issues:
    • Spark Plugs: While 45,000 miles might seem early, worn or fouled spark plugs can definitely cause a rough idle and misfires. They are a relatively inexpensive and easy first check.
    • Ignition Coils: A failing ignition coil can cause intermittent misfires that might not immediately trigger a CEL, especially if the misfire count is low.
  2. Fuel System Problems:
    • Dirty Fuel Injectors: Clogged or dirty fuel injectors can lead to an inconsistent fuel spray pattern, causing a lean condition in one or more cylinders and a rough idle.
    • Fuel Pressure: Low fuel pressure from a failing fuel pump or a clogged fuel filter (less common on newer vehicles with lifetime filters, but still possible) can starve the engine of fuel.
  3. Air Intake System & Vacuum Leaks:
    • Mass Air Flow (MAF) Sensor: A dirty or faulty MAF sensor can send incorrect air intake readings to the ECU, leading to improper fuel-air mixture.
    • Throttle Body: A dirty throttle body can restrict airflow at idle, causing rough idling and stalling. Cleaning it is often a simple DIY task.
    • Vacuum Leaks: Leaks in vacuum lines or intake manifold gaskets can introduce unmetered air, leading to a lean condition and rough idle. Listen for hissing sounds.
  4. PCV System: A clogged or faulty PCV valve can affect engine vacuum and cause idling issues.

When to see a shop:

  • If cleaning the throttle body and inspecting for obvious vacuum leaks doesn't resolve the issue.
  • If you suspect ignition coil or fuel injector problems, as these require more specific diagnostic tools (e.g., oscilloscope for coil patterns, fuel pressure gauge).
  • If the problem worsens or a CEL eventually illuminates. A professional shop can use advanced scan tools to monitor live data, perform cylinder balance tests, and pinpoint the exact cause more efficiently.
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