Back to the original topic:
Took another test today after last weekend's big service and the tightning of the 3 nuts that were loose between exhaust manifold and pipe.
First the HC was steady around 250 (still too high, 200 limit) but after a while it went up around and over 1000 again.
The idle is slightly worried from the EB 261C cam shaft so it's quite hard to get a steady reading.
Gonna remove the cat this weekend and see what it looks like...