That could be it, the inlet manifold was replaced recently as had a hole on the top; it used to splatter oil out of this occasionally so there must have been a fair amount in the inlet. Thanks for the pointer.

Hi, I’ve had a diesel 99 p38 for the last six months and fixed many things :D. The ride performance is excellent out here in the country with the rough lanes to navigate. But one problem does not seem to go away, in that every so often when I switch it on the throttle races up to full, black...