2001 X reg 1.9 TDI, changed fuel filter 400mls ago & have noticed air in clear fuel line, when reving engine there seems to lots of large bubbles, car runs o.k. except on start up when it appears to misfire which it did not do with old filter, but soon clears, cannot recall seeing air in previous filter but i only had car a few days before i changed it, any help appreciated

The clear pipes always do have air in them. Did you replace the two O rings on the plug in part of the filter pipes?