Whooo hooo got one right, Richard i had the same fault on my pug 607 hdi , the fault on my 607 was the vaccum solenoid was at fault and the vaccum was leaking from the bottom of the solenoid so the flap wasnt getting opened on cold start, the 607 had the dozer valve on the manifold (2 seperate flaps) vaccum opens one of them whilst the other vaccum closes it , just a little info for you .
Lee