Focus 1.8 TDCi Sport - Red Warning Light

[FirSTFocus]

Hi,

I hope someone is able to help me. I have just bought a 2006 (06) Focus 1.8 TDCi Sport and when I bought it, all seemed fine. However, when the car has sat for a day or two, and I first start it, I get the red engine warning light come on and the car runs a little roughly. 

Each time this has happened, within two minutes, the warning light has gone out and the car has run fine and presented no more problems, no matter how far my journey is.

I realise it is a bit like going to the doctors and saying, "I have a cough, what could it be?" but I hope someone can help.

 

Thanks in advance.