The BlueTack remedy on the EGR valve resulted in a significant improvement. In fact so much so that the dashboard engine management light turned itself off for a short period. However, under hard acceleration the car could still generate considerable smoke (to the annoyance of cyclists!) and a replacement EGR was necessary.
An EGR valve has now been obtained from H.R. Owen, North Acton, London via eBay (and who provided excellent service to resolve problems with the delivery). Although it's fitted I've only been able to take the car a short test run as yet. What I'm eager to do is collect the engine data with Torque and see if the air flow/ manifold pressure etc now generate a more orderly pattern of results.
