Ford Focus Attemping To Turn Off Itself

Hi guys.

I have a ford focus TDCi 2003 which is having some issues when car is cold.

the car is starting ok but it attempts to turn off, this issue happen only when the car is cold. after the car is warmed up the problem dissapear.

It attempt to turn off when driving and even when i am on parked and turn the engine on i can listen carefully the accelerater is changing itself, and you can tell the car is trying to turn off and go back to normal.

i have took the car in a service and they found on a computer diagnostic there was an injector fault. i have changed the injector but nothing changed in the problem as it still does it, its very dangerous as it can turn itsself off while i am driving.

if i leave the car on for a while (normally 20-30 mins) it runs ok after that but the problem seems to be only when the acr is cold.

anyone knows whot this could be and how should i fix it?

any help will be approchiated.

thanks