Volvo V70 - Engine cutting and erratic rev counter

Hey guys, I promised my parents I'd post up on here as you're all such a mind of information and they're getting a bit fed up.



They've got a 2005 Volvo V70 (diesel estate) and they have an intermittent issue.



You can do 100 miles without ever encountering any problems then randomly the car will just suddenly start shuddering and trying to cut out. Whilst this is happening the rev counter bounces up and down erratically.



If you take your foot off the accelerator the car will eventually stall and sometimes refuse to start for a short time afterwards but if you keep your foot on the gas the car usually recovers before this happens and will then usually go fine again for another 100 miles or so.



They've had a full service and new fuel filter, the injectors refurbished and they've also had the intercooler refurbished at the recommendation of their garage but given the way the rev counter is behaving I'm inclined to think they've got an electrical issue; a dodgey sensor or an issue with the ECU wiring.



Has anyone got any ideas as to what this is likely to be? There don't seem to be any codes on the car (which makes me wonder about sensors) and the engine light has never come on.



Any and all advice welcome as always, thanks guys! :)

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