Mitsubishi i - Surging and slowing when cold - Brubaker

My automatic "i" has done 34,000 miles, it has a full Mitsubishi service history and I have reviewed it for HJ. It has just developed a disconcerting fault when driving from 'cold' and I would appreciate some advice before entrusting it to our local (not particularly good and expensive) dealer. For the first couple of miles it will do as follows. Drives off OK but then you will find the car does not accelerate - no matter how much you depress the 'throttle' pedal. Then it will suddenly 'surge' and leap away. If you keep a relatively constant throttle it will do all this on it's own with no further throttle input. Going slowly, leaping away and slowing again. Once 'warmed' up (couple of miles or so) it's fine and remains so throughout the day. It has never been used on really short journeys always at least 5 or 6 miles and more likely 30-60 miles.