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2021 S5 Sportback Loss of Power and Rough Idle - Carbon Buildup?

0

Mike T. · rep 0 · May 25, 3:11 AM · 1 replies · solved · Question

Vehicle: 2021 Audi S5 Sportback 3.0T

Hey everyone,

I'm posting about an issue with my 2021 Audi S5 Sportback, 3.0T engine. I've noticed a gradual but definite loss of power over the last few months, and the car doesn't feel as responsive as it used to. The idle has also become a bit rough, not terrible, but noticeable. Fuel economy seems to have worsened slightly too.

I've read a lot about carbon buildup being a common problem with direct injection engines, especially on older Audi models. Could this still be an issue for a 2021 model year with the 3.0T? I don't have any Check Engine Lights currently, but the performance degradation is concerning. Has anyone with a B9 S5 experienced similar symptoms that turned out to be carbon related?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 3:11 AM

0

ClearTheCode admin answer:

Your symptoms of gradual power loss, rough idle, and decreased fuel economy in a direct-injection 3.0T engine are highly consistent with carbon buildup on the intake valves. Even newer models like your 2021 S5 are susceptible, though it might take longer to manifest compared to earlier generations.

Causes of Carbon Buildup:

  1. Direct Injection Design: Unlike port-injected engines where fuel washes over the intake valves, direct injection sprays fuel directly into the combustion chamber. This means the back of the intake valves are never cleaned by fuel.
  2. PCV System: The Positive Crankcase Ventilation (PCV) system vents oil vapor and combustion byproducts back into the intake manifold. These oily vapors, combined with exhaust gas recirculation (EGR), bake onto the hot intake valves, forming hard carbon deposits.
  3. Driving Habits: Frequent short trips or prolonged idling can exacerbate carbon buildup as the engine doesn't reach optimal temperatures to burn off deposits as effectively.

Impact of Carbon Buildup:

  • Reduced Airflow: Deposits restrict airflow into the cylinders, effectively reducing engine breathing and power.
  • Turbulence: The rough surface of the carbon creates turbulence, hindering efficient air intake.
  • Misfires: Severe buildup can cause misfires (P030X codes) if the valve doesn't seal properly or airflow is too restricted.
  • Lean Conditions: Can sometimes lead to lean codes (P0171/P0174) due to disrupted airflow.

Diagnostics & What to Do:

  1. Visual Inspection: The most definitive way to diagnose carbon buildup is a visual inspection using a borescope inserted through the intake manifold. This will clearly show the extent of the deposits.
  2. No OBD Codes: It's common not to have specific OBD codes for carbon buildup itself. Codes like P030X (misfires) or P017X (lean conditions) might appear if the buildup is severe enough to cause other issues.

When to See a Shop:

  • Recommended: If you're experiencing noticeable performance degradation, it's time to have your S5 inspected. A professional Audi specialist can perform the borescope inspection.
  • Carbon Cleaning (Walnut Blasting): The most effective solution for carbon buildup is a procedure called walnut blasting. This involves removing the intake manifold and using specialized equipment to blast crushed walnut shells at high pressure to remove the carbon deposits from the intake valves. This is a labor-intensive but highly effective process that can restore lost power and smoothness. It's not a DIY job and requires specialized equipment and expertise.
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