Hi guys , i ve picked up a fiat linea 2010 petrol on the 1st of feb. After driving the car for a day or two I noticed that between 1800 to 2200 rpm the engine practically stalls and gathers speed in a very jerky motion as if the hand brake has been pulled and there is too much of a load ..Once i am close to 2500 rpm , it runs smoothly. This happens mostly in 3rd and 4th gear. If however i change my gears at a higher rpm , the engine is not jerky but gathers speed very slowly. What could be the problem?The cars done only 250 kms till now.