VAUXHALL STALLING

[RAVEN 456]

I have a couple of works Vauxhalls, one of the Combos once a month or so starts rev hunting around 1000 rpm, then it stalls when coming to a stop but still moving so it's the rev drop not the start/stop system. The DPF light comes on, but this has been cleaned and tested and is fine. After this happens around 3 to 4 times one after another the problem goes away, the engine is smooth, drives great and them maybe a few weeks later this problem re-emerges.
Have replaced cam position sensor, just about to replace crank sensor but I don't think it's either of those at fault.
Any ideas anyone?

Thanks