how to fix my ford escort diesel van?

On the first start of the day my 1996 ford escort diesel 1.8 turns over for ages and struggles to start,once it hopefully starts it lets a cloud of grey/whitey smoke and then its fine for the rest of the day,ive changed the heater plugs and tested the current,checked the cold start relay,new fuel and air filter but to no avail.it seems to start a bit easier if when turning over you hold he trottle to the floor and let it off just as the engine fires,once a warm start is required i dont use any throttle and it starts fine.i no of a couple of identical vans that have the same problem,pleeeease help its realy annoying