Hi
Thanks all for the replies.

not had much time to look today, just snatched 1/2 hour before closing.

Slackened the fuel cap off, and on road test fault was only just noticeable (not perfect), much less so than yesterday, not sure if that is just coincidence.

Checked fuel flow rate (good ) and for air content OK. this was workshop test, not ideal, but unable to flow test road test. ( this has no return from rail )

Pete despite high mileage, no undue breathing. not done compression test yet, but sweet as a nut at idle and due to intermittent nature, unlikely to be mechanical i feel . Does not feel like a sticking valve.

Sean thanks for info on air mas voltage, confirms my reluctance o condemn it

James, I am interested in you comment on throttle unit,This is an area i have been considering. I have cleaned it. Do the symptoms fit with your experience ?

Cheers Aidan