The S65 uses individual throttle bodies (ITBs) with electronic actuators. The small DC motors that control the butterflies wear out, causing erratic throttle response or complete failure. BMW sells them only as a complete set.
Symptoms
Check engine light, reduced power mode (limp mode), rough idle, hesitation on throttle application
Fix / Remedy
Replace all throttle actuators as a set. Aftermarket options available at lower cost. Recalibrate throttle adaptation values after replacement.