Hello Emrys, did you go to the guys are based in Taunton ? I had problems with egr valve and dpf filter. In my case it was too late for regeneration but Peter managed to remove dpf , clean egr and clean intake system and injectors with his new toys. The car never drive better than today. Recommanded to all.So if you having problems with you IS220 don't hesitate to contact them - they know waht they are doing.
Regards.