During the GBS trip I decided to do an instrumented run to check the lambda sensor. I noticed straight away she didn't go into closed loop so after a few miles, while at some traffic lights, I stopped the engine, counted to 10 and restarted her (good thing we don't suffer from the hot starts any more). She quickly went into closed loop and stayed there for the rest of the trip there.
Here's the trace. As we can see she was scruffy as old boots until the restart and then absolutely fine.
On the way back the same thing happened, except this time the first attempt at restarting didn't help. It was a second, later, attempt, again at some traffic lights, that made the difference.,
So what can we deduce from that ? Although the sensor could be going soft, my first thought is that the heater is not working properly. As we know my wiring is not the best in the world 😁 I guess while I have the soldering iron out I can redo all the lambda heater joints. I'll see how that goes. But there's no mad rush as I don't need it working till the emissions test in August.