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Rough Idle & Hesitation on 2018 XC90 T6 - Time for New Plugs?

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Chris P. · rep 0 · May 22, 5:17 AM · 1 replies · solved · Question

Vehicle: 2018 Volvo XC90 T6

Hey everyone,

My 2018 Volvo XC90 T6, with about 75,000 miles on it, has started to develop a bit of a rough idle lately. It's not super severe, but I can definitely feel it, especially when stopped at a light. I've also noticed a slight hesitation when accelerating from a stop, almost like it's struggling for a split second before catching on.

I haven't seen any check engine lights yet, but I'm wondering if this could be related to the spark plugs. I don't think they've ever been changed since I bought the car used a couple of years ago. The owner's manual suggests a pretty long interval, but I've heard that for the T6 engine, it might be good to do them a bit sooner, especially with these symptoms.

Has anyone else experienced similar issues with their 2016-2026 XC90 T6? Is this a DIY job that's manageable for someone with moderate mechanical skills, or is it better left to the pros? Any specific tools or tips I should be aware of if I decide to tackle it myself? Thanks in advance!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:17 AM

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ClearTheCode admin answer:

It sounds like your 2018 Volvo XC90 T6 with 75,000 miles is showing classic symptoms of worn spark plugs, which can definitely lead to a rough idle and hesitation. While Volvo's recommended interval for spark plug replacement on the T6 engine (B4204T27) is often around 60,000 miles or even higher in some markets, driving conditions and fuel quality can influence their lifespan. It's a very common maintenance item that can significantly improve engine performance and fuel economy.

Here's a guide to help you:

  1. Diagnosis Confirmation:

    • Even without a Check Engine Light (CEL), a misfire might be occurring intermittently. If you have access to an OBD-II scanner, check for pending codes (P030X, where X is the cylinder number) or misfire counts. This can help pinpoint if a specific cylinder is struggling.
    • Visually inspect the ignition coils for any signs of cracking or oil leaks, as a failing coil can mimic spark plug issues.

  2. DIY Feasibility:

    • Replacing spark plugs on the T6 engine is generally considered a moderate DIY job. You'll need basic hand tools, including a torque wrench, spark plug socket (typically 14mm thin-wall for these engines), and extensions.
    • The engine cover needs to be removed, and then the ignition coils for each cylinder. Take care when disconnecting electrical connectors.

  3. Recommended Parts:

    • Always use OEM-equivalent or specified spark plugs. For the T6 (B4204T27) engine, Volvo typically uses NGK or Denso iridium-tipped plugs. Double-check your owner's manual or a reputable parts catalog for the exact part number.
    • Consider replacing the ignition coils if they are original and have high mileage, or if you find any signs of damage during inspection.

  4. Procedure Tips:

    • Ensure the engine is cool before starting.
    • Remove one coil and plug at a time to avoid mixing up components or dropping debris into open cylinders.
    • Apply a small amount of anti-seize to the spark plug threads (optional, but recommended by some) and dielectric grease inside the coil boot.
    • Torque the new spark plugs to the manufacturer's specifications. Overtightening can damage the cylinder head, while undertightening can lead to blow-outs.

When to See a Shop:

  • If you're uncomfortable working with engine components or lack the necessary tools.
  • If, after replacing the spark plugs, the symptoms persist or worsen, or a persistent Check Engine Light appears. This could indicate a deeper issue, such as a failing ignition coil, fuel injector problem, or even a compression issue, which requires professional diagnostic equipment.
  • If you encounter any stripped bolts or broken connectors during the process.

Addressing this maintenance proactively will likely restore your XC90's smooth operation.

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