[ainarssems]

Removing swirl flaps will not affect full throttle performance as they are fully open at high load. They are there for fuel economy and emissions at idle/part load. What they do is partially close one of intake channels in manifold for each cylinder so that airflow amount and speed is different in each channel, this causes air to swirl more as it enters the cylinder, mix better with fuel and result in cleaner combustion. At WOT they are open to get more air almost like if they were not there.

I know they unbolt in BMW's and end up in engine, not sure if that's the parts that get sucked in 4.0TDI' as there are also throttle flaps and I have heard people blaming the fact that manifolds are plastic so maybe plastic fractures and send bits in engine. If it's just swirl flaps then it could be simple solution. If they are getting loose it might be possible to service them, use thread lock on any bolts and screws or weld them together or possibly replace by custom made parts if they wear out. It's a bit harder if manifold itself fractures and breaks down.