WHATS WRONG??

I have a Y reg escort deisle van. When i first start it on a morning it runs as though there is a fuel shortage. It runs fast then slows down, then speeds up.Its the same when i drive. When she warms up it improves a lot,but there is still times i can feel her run faster then slower. I have checked the fuel and ther is no blockage or water in the fuel or filter. Please can some one help before i ripp my lips off. Thank you,
Nev Robson. Northumberland