I think that running an inlet valve cleaner damaged the cat. I think that the bad running last October was a partial internal collapse of the cat. It's certainly curious that now I can't really feel any difference but the tailpipe is black, as it always was in the first two years. Really this is typical of Morgan where two identical cars behave differently. Just look at the rev hang that some Roadsters get, but not all of them!
Absolutely agree on identical cars behaving quite differently. My GDI in bog standard fettle never suffered a hair trigger throttle and pulled consistently from low revs. Pre Club Sport fitment I used inlet valve cleaner both before and after removing the manifold to inspect and clean the valves. In standard trim it never had difficulties at MOT, apart from the 1st time when the engine was presented virtually cold. Now I make sure it arrives for testing stinking hot.
Last MOT - ie with Club Sport fitment - although it sailed through the slow idle test, it recorded 0.178 against a max 0.200 in the fast idle test.
Have just ordered the 02 sensor spacer suggested by Grumpy2 and shall also look at a temporary tailpipe cross section reducer. Just in case...
