Problems with Vauxhall Vectra 1.9CDTi 150bhp 6 Speed Manual (2008)?

Can anyone help me with the following problem I'm having.
The car is "hunting" when it's stationery, basically it's sounding like a tractor, and chugging rather than purring, I've had a look on other forums but I'm getting no specific details in responses, everyone seems to mention number 3 injector problems.
All the battery, oil, etc are fine, so the cause is a mystery to me.
Thanks