Renault scenic 2005 1.5dci low power problem and fuel funnyness

everything worked perfectly fine until one day half way through her travels she put her foot to the floor and the response and rev increase was really slow, if the car is parked up and you rev it no problems, under further investigation i have noticed we have this loss of power when traveling at 30+ mph or when the engine is under load, i have removed and cleaned the egr valve and piping, which mate roughly 25% power com back, my next action was to replace the fuel filter, under further inspection i noticed that the fuel supply line had large air bubbles in it, this is between the primer bulb and the fuel filter, you can only see thease air bubbles when the engine is switched off and the fuel flows backwards through the line, the air bubbles come from the fuel filter and go to the primer bulb and stop there, also i have noticed when the engine is running the fuel return line as a large amount of small bubbles coming through every once in a while, any help is greatly appreciated

Renault scenic 2005 1.5dci low power problem and fuel funnyness