c5 running problems

Hi, i have a citroen c5 estate 2003 hdi. when i i leave the car for a few hours or more it starts 1st time but it has no power when i try to accelerate. This happens for the 1st 5 minutes of the drive and then all of a sudden the power will come back. This has been happening for about a month now. I have put a new battery on and glow plugs. Can any one help me get to the bottom of this please?

Any 1 any help please?

Yep mine went like that until it lost power all of the time, there is a tank containing a fluid around the rear wheel area accessed behind a premovable panel I believe it need to be filled occasionally with Addictive System Fluid, it's part of the Pollution Control system, also used on more recent Peugeots such as the 407 oh its LH side looking from drivers seat hope that helps