2.0iDT Rover 25 van 'missing' ....odd for a diesel??

OK, this may be a stupid question.... I have just noticed that when I rev my commerce 25 van slowly from 900 to 2000/2500 rpm it appears to be 'missing' for all the world like as if a spark plug is breaking down.



Anyone have experience of what this could be?



All help appreciated





Thanks

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