I have a peugot expert 1998 that is dificult to start. Glow plugs have been replaced fuel filter new. when I eventualy get her started she runs rough on tick over when reved it runs better. If I loosen off the banjo union on top of the injector pump the fuel return the fuel coming out is like foam with lots of air in it. I have checked the supply and cannot see any air going into the pump. If I pump the bulb primer pump she runs smoothly. To me this sounds like injector pump problems is this repairable or would I need a new pump!!!!!