The fastening of the swirl flaps in the intake works loose from the vibration of the engine, and a flap can come away. From there it gets through the intake into the cylinder, and takes the piston and the valves with it, so the cost of the repair ranges from the price of a flap to an engine rebuild. The older units with metal flaps are the most dangerous. The symptoms are a rough idle, a loss of power and occasional juddering, with the code P2015 in the fault memory. On the M47TU2 this is the most common case. Prevention comes in two forms. Either a reinforced flap is fitted, aluminium or assembled with thread-locking, or the flaps are taken out and blanking plates go in their place. The second is the more radical one and takes the risk to zero; many workshops recommend it, and the airflow does not suffer from it either.