Darren- it might be worth smoke testing the inlet circuit. The 271 engine has a small breather hose that goes soft & ruptures. You cannot see it with the air filter housing & air mass meter in place but smoke pouring out from the underside is enough to warrant taking apart & having a look. Also if you can check the adapted engine values you might find they are out of range- particulary at idle. If the hose is the fault- you will have to reset the adapted values after it's been replaced.