Strange Engine Surge

Hi all,I've got a 1.6 petrol focus (zetec) it's only 2 tears old so still under warranty but just so as i might get an idea as to what to may be happening here are the symptoms. When in 2nd or 3rd gear and turning, the engine surges slightly,this only happens as the steering wheel is being turned and is most noticed when going around a traffic island, it makes no difference whether my foot is on or off the gas . Also when the car is idling it gives sporadic shudders, more noticeable if its done a long run and the engine is hot. I've had it in once to check for misfiring but everything is fine on that point(the mechanic wasn't v helpful when i told him the other symptoms) It's been suggested that the idle valve may be to blame or one of the sensors but any other suggestions would be appreciated so i can throw a few of them to the ford mechanic when i take it back in. Thanks. Adz37.