i aint much up on new diesels but ur describing classit air starvation problem renew your air filter for one also check a small bird/object hasent been suked into air intake bloking it . the bird being suked in was a real situation i came across on a friends peugeot 309 diesel wich evaded trained peugeot technitions for nealy 1 week they had the whole fuel system apart to no avail. i just went back to basics.
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