Im having some minor problems on my Ford Focus Zetec 06 27.000 miles. I did a full service on november 2010 but from 1 month is doing a bit of jerking on 2nd gear at low speed/2000 revs. then dissapear when i go to higher speeds. It is only a small jerk but also i notice that have lost some power on hills in 1rst / 2nd gear specially..

No warning lights on the dash and other than that car is working perfect and i love it!! pulling strong on 3rd 4rd and even 5th gear.

On the full service done by a Ford specialist was changed the spark plugs.. I though that was a petrol issue but now im filling up the car with Shell VPower 99 and the car pulls quicker but still some jerking sometimes after stop on traffic lights specially..

Im not very concern about this problem as is not impacting on the normal drive of the car, but should i be worry?

Thank you for any answers..