Wont start when cold and loss of power

From a cold start the engine turns over but does not seem to be firing, it takes several attempts and a lot of pedal twitching to get it going, very low idling below 80 degrees C then idle is OK.
Once runninng acceleration judders with loss of power (foot can be flat to the floor in second gear with hardly any power)
When on the motorway there is not enough power for overtaking.

This problem began the day after we had a new manifold fitted, don't know if this is the cause of the problem or not.