Well since NO ONE replied on this...
Should have caught it - the timing chain rattle noise.
I think she may have skipped a tooth already and the computer was doing its best to manage the timing. Alas the poorer fuel mileage.
315,000km and engine is toast.
Chain skipped again on starting and valves bent.
Putting in yard engine with 143km. Back on the road shortly.
New engine cheaper than my recent catalytic! (course I am doing this myself)