My Xf has a problem

When i start it when its cold it runs really rich and it will conk out occasionally or sit at the point where its about to.

So i had a look at it tonight. I started it cold and jammed open the butterfly with a screwdriver and it ran really well.

My question is why is that so? I have disconnected the butterfly and it runs really well

Any help would be good

wouldnt be the first time the electric choke in an XF s**t itself......

either disconnect it or leave it at a mech who knows his s**t so he can sort it out 1st thing in the morning