2003 Renault Clio Renault Clio 1.5 DCi 2003

Hi, my Clio Diesel sometimes stops/stalls, it's just like someone has turned the ignition key off,.
i can see Air in the low pressure fuel pipes,
fuel going into the pump from the filter looks ok, fuel coming from the pump to the return feed has air bubles in, i have bled the fuel system & primed it twice ??