I've got a Mk3 2.0tdi 184 which randomly takes a good few seconds to start. Sometimes it fires up straight away and sometimes it doesn't. The battery is in good order and I doubt it would be the glow plugs due to the warm weather. I'm going to change the diesel filter as i'm unsure when that was last done but doubt that will make too much difference. No fault codes stored on the OBD port. When driving it's perfect with no power loss or anything.