Air in fuel pipes is normally caused by one of three problems..
1# leakage in pipes or connectors (air gets through gaps that are too small for fuel to get through so no leakage is apparent)
2#Fuel pump is faulty
3#Swirl pot is broken/bypassed (see fault below), thus not picking up fuel from the pot but relying on the tank level (swirl pot prevents side to side movement of the car putting air into the pipes)
Have you recently had the pipes changed?? If yes then it could be a simple fault caused by the pipes being swapped round with the feed pipe connected to the return connector and vice-versa.. Had this one time on a combo van.. would run for a bit then cut out..then repeat
