What are the normal warning signs of failing swirl flaps on a Vauxhall Astra?

My 2007 Vauxhall Astra 1.6 petrol engine was wrecked by the swirl flaps, with no obvious prior warnings. In last Saturday's Telegraph a garage identified a failed inlet manifold and swirl flaps. How is this possible?
The reader wasn't very specific so I had to assume that what he meant were the swirl flaps. The operation of the swirl flaps can be checked during a normal diagnostic tune-up.
Answered by Honest John on

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