Lumpy idle

Having a few issues with my td4 2003,
When I start car runs like its misfiring and juddering like mad white smoke (smells of diesel)
Have changed crankcase filter, air filter, fuel filter and cleaned egr valve
And had a bottle of injector cleaner.
Runs fine when under load and pulls well
Also has difficulty starting after a long journey engine turns over but like no fuel.
Could this be the low pressure pump failing?
Or would I be better off getting the injectors tested?
Many thanks

Listen for the LP pump at the rear wheel arch working when it wont start, if its ok do an injector leak back test.