Hi all, im new to the forum.

ok, im not the best with cars apart from knowing how to rebuild pushrod engines

anyway im having problems with my w210 e300 diesel [non turbo].

the problem has been going on for over a year now,
the symtoms are -

1. it takes a while to start in the mornings.
2. it cutsout on long [motorway] drives,it will throw out blue smoke before cutting out.
3. at idle the engine will randomly run smooth then ruff[engine wobble]

around 3 month ago i thought i cured it as i noticed air bubbles travelling in the pipes going to and from the fuel filter.
so i replaced the fuel filter and all related rubber washers on the fuel filter housing.
now this seemed to sort it out and has been running as sweet as a nut since then. but the air bubbles are back!!
ive changed the fuel filter and housing washers again but this time it hasnt sorted the problem and the air bubbles are still there.

im sure the bubbles are the problem!? but im unsure of where else to look besides fuel lines