The intake manifold's swirl flaps can fail, and on higher-mileage cars the hardware can be ingested; a 'flap delete' for a few hundred dollars is the common preventive fix versus a ~$3k manifold. It's genuinely debated — some owners prefer leaving it stock, noting deflapped cars can run rough when cold.
Intake-manifold swirl flaps: the 'de-flap' question
Audi RS4 (B7) · mechanical