Modern diesel engines — especially Euro diesel vehicles like BMW, Audi, Volkswagen and Mercedes-Benz — commonly suffer from carbon accumulation due to: EGR (Exhaust Gas Recirculation) systems Oil vapour from the PCV system Soot recirculation Short-trip driving conditions Over time, thick carbon deposits restrict airflow inside the intake manifold and intake ports. This can lead to: Rough idle Reduced power Sluggish throttle response Poor fuel economy Increased smoke Engine he