my vehicle is not working

my car peugeot 206 hdi x-line 2004 model. My vehicle does not work like this. In these cases, I open the engine cover and tighten the thing like the pump there. After a while, it either works or does not work according to the vehicle head. but it usually works after doing this operation. I ask you why this problem may be caused by giving an answer to this, and if this failure happened to someone else before, how much would it cost? If it is high, I will either sell the car or burn it by pouring petrol. I am waiting for your valuable information. thanks in advance