Rough Idle on Diesel Toyota

[ffzetecs]

Hi,

Have an Auris diesel with an intermittent issue of rough idling - occasionally the needle jerks between 600-800 rpm

Had the EGR valve cleaned and fuel filter replaced 20k ago.

Hard to diagnose with garage as it's intermittent.

Been advised it could be carbon build up.

However, I'm getting good fuel economy and I do mainly motorway driving.

Any thoughts appreciated.