[Brightside]

Hello all, my 2013 S60 D4 163bhp 5 cyl has recently developed an intermittent fault. It used to deliver upwards of 50mpg with ease all the time, but now I'm struggling to get above 40mpg. Sometimes it runs fine still, but at other times it takes a big hit on the fuel consumption. When it's running fine it'll idle at 0.1gph, but when it's running bad it idles at 0.3-0.4gph. I know when the car is doing a dpf regeneration and its not that. With it being erratic I was thinking a sensor might be faulty, but I wouldn't know where to begin. Can anyone point me in the right direction of where to start looking/checking please? Thanks in advance of any replies.