Blimey, this was a long time ago now. The Fiesta is long gone now, replaced by a MK6 Zetec S Fezza, then a Civic Type R, and currently a Focus ST2.

Anyway, just to close the book on the Fiesta fault - it turned out to be a split vacuum hose underneath the inlet manifold. After tearing my hair out with everything else a simple repair with super glue and gaffer tape sorted it out and the car ran perfectly for the rest of the time he owned it - and all of the time my sister owned it after him.

Now my time is spent looking after my ST170..............