NON VAG diesel issue.

I currently have a Pug 306 HDi in my possesion

it gets left a week or 2 without being ran

when it does get started it BELLOWS bacl , thick black sooty smoke out.

Then when taken for a run is eventually turns to a thinner grey smoke, but again bellows out a huge cloud of greyer smoke for ages - enough to make the car behind dissappear

eventually it clears itself to a standard smokey old pug diesel kinda smoke

So, is this just cos its getting left week in week without use ?
thanks in advance