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Rough Idle & Misfires on 2017 Q5 2.0T - Carbon Buildup?

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Emily N. · rep 0 · May 22, 4:30 AM · 1 replies · solved · Question

Vehicle: 2017 Audi Q5 2.0T Premium Plus

My 2017 Audi Q5 2.0T (B9 generation) with about 70,000 miles has been acting up lately. I've noticed a rough idle, especially when cold, and sometimes it feels like there's a slight hesitation or misfire under light acceleration. The fuel economy also seems to have dipped a bit.

I haven't seen a Check Engine Light yet, but I'm worried it might be carbon buildup on the intake valves. I've heard this is a common issue with direct-injection engines like mine. Has anyone else experienced this with their Q5 or similar Audi models?

What are the typical symptoms of carbon buildup, and what's the recommended solution? Is this something I can try to address with fuel additives, or is a more invasive cleaning necessary? Any advice on diagnostics or next steps would be great.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:30 AM

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ClearTheCode admin answer:

Carbon buildup on intake valves is indeed a very common issue with direct-injection engines, including the 2.0T in your 2017 Audi Q5. Without fuel washing over the intake valves, carbon deposits from PCV blow-by can accumulate over time.

1. Common Symptoms of Carbon Buildup:

  • Rough idle: Especially noticeable when the engine is cold.
  • Misfires: Can occur under various conditions, leading to hesitation or a feeling of power loss. May trigger OBD-II codes like P0300 (Random/Multiple Cylinder Misfire Detected) or specific cylinder misfire codes (e.g., P0301 for cylinder 1).
  • Reduced engine performance: Less power, slower acceleration.
  • Decreased fuel economy.
  • Check Engine Light (CEL): While you haven't seen one yet, persistent misfires will eventually trigger the CEL.
  • OBD-II Codes: Besides misfire codes, you might also see codes related to lean conditions like P0171 (System Too Lean Bank 1) if the buildup is severe enough to restrict airflow.

2. Recommended Solution: Walnut Blasting:

  • Unfortunately, fuel additives are generally ineffective against significant carbon buildup on the intake valves of direct-injection engines because the fuel doesn't touch the valves. The most effective and recommended solution is walnut blasting.
  • This process involves removing the intake manifold and using specialized equipment to blast crushed walnut shells (a non-abrasive medium) at the intake valves to remove the carbon deposits. It's a thorough and safe method.

3. When to See a Shop:

  • Walnut blasting is a labor-intensive procedure that requires specialized tools and expertise. It's not a DIY job for most home mechanics. You should take your Q5 to an experienced independent Audi specialist or an authorized Audi dealership. They can perform a proper diagnosis, often using a borescope to visually inspect the valves, and then carry out the cleaning procedure correctly. Addressing this issue can significantly restore your engine's performance and efficiency.
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