01 jetta tdi will not start if the car is parked for more than about two days. it will just turn over and over. noticed that the clear line on top of the fuel filter is not filled with fuel but instead air. so i guess this is the problem but how would the fuel system be getting air in and loosing prime. i can start the car with starting fluid and it will eventually start and then run fine, but if you don't crank it like every day it won't start. please help!