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Rough Idle and Misfire on my 2018 XC90 T6 - What's going on?

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Kevin B. · rep 0 · May 22, 5:12 AM · 1 replies · solved · Question

Vehicle: 2018 Volvo XC90 T6 Momentum

Hey everyone,

I've been experiencing a really rough idle on my 2018 Volvo XC90 T6 lately, especially when the engine is cold. It feels like the car is shaking a bit, and sometimes I notice a slight hesitation when accelerating from a stop.

The check engine light came on a few days ago, and when I scanned it, I got codes like P0301 (Cylinder 1 Misfire Detected) and P0300 (Random/Multiple Cylinder Misfire Detected). I'm worried this could be something serious.

Has anyone else with a T6 engine experienced this? What were your solutions? I'm trying to figure out if this is a common issue before I take it to the dealership.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:12 AM

0

ClearTheCode admin answer:

Rough idle and misfire codes (P0300, P030x) on a Volvo T6 engine, especially a 2018 model, can stem from several common issues. The T6 engine is known for its complexity with both supercharging and turbocharging.

Common Causes:

  1. Ignition System Components: Worn spark plugs or failing ignition coils are very common culprits. Over time, spark plugs degrade, and coils can develop internal shorts, leading to weak or no spark in a cylinder. Given your codes, this is a prime suspect.
  2. Fuel System Issues: Clogged fuel injectors can cause a cylinder to run lean or rich, leading to misfires. A failing fuel pump or a clogged fuel filter, though less common for specific cylinder misfires, could also contribute to overall fuel delivery problems.
  3. Vacuum Leaks: Leaks in the intake manifold or vacuum lines can introduce unmetered air into the engine, disrupting the air-fuel mixture and causing rough idle and misfires.
  4. PCV System: A failing PCV (Positive Crankcase Ventilation) valve or a clogged PCV system can lead to excessive crankcase pressure, potentially causing oil leaks and affecting engine performance, including misfires.

What to Do:

  1. Check Spark Plugs and Coils: This is the most straightforward first step. Inspect the spark plugs for wear and tear. If they haven't been replaced recently (typically every 40,000-60,000 miles), consider replacing them. You can also swap ignition coils between cylinders to see if the misfire code follows the coil, indicating a faulty coil.
  2. Inspect for Vacuum Leaks: Listen for hissing sounds around the engine bay, especially near the intake manifold. A smoke test performed by a mechanic can pinpoint elusive leaks.
  3. Fuel System Diagnostics: If ignition components are ruled out, a shop can test fuel pressure and injector performance.

When to See a Shop:

If you've checked the basic ignition components and the problem persists, or if you're uncomfortable performing these checks yourself, it's best to take your XC90 to a qualified Volvo specialist or dealership. They have specialized diagnostic tools (like VIDA) that can provide more in-depth information about the engine's operation, pinpointing the exact cause of the misfire. Continuing to drive with a persistent misfire can damage the catalytic converter due to unburnt fuel entering the exhaust system.

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