vw sharan it an s plate?

hi i have a vw sharan 1.9 petrol but im having a problem starting it in the morning but after about the thured turn of the key it starts but but the engine shackes bad for about ten seconds but the ok all day i was told to try and change the power sterring spring first because it has worn would that be the problem or do you think it could be some think diffrent and is it easy to do by my self