Hi John, I did sort it mate! Did two things. Changed the O-rings on the intake air control valves and changed the spark plugs. I reckon it could just have been plugs as the ones that came out were in a state and likely the original plugs first fitted that would have now done some 85,000 miles! Drives like new since, happy days! Good luck with your own and do let me know if yours might fix the same way.