Weird uneven tickover problem starting about 30 seconds after starting and lasting about a minute. It's very consistent and has been doing it for many months.

I like to get to the bottom of minor things like this because they often precede something worse.

I don't have a good ear for V8s. Might be a misfire but that would start straight away, wouldn't it?

Runs OK on open loop, then goes to closed loop and takes 30s to re-set the trims correctly? Just a guess, and probably wrong.
You might have some codes in your motronic to help you narrow this down.

I would guess the same as Morat, I've seen plenty with broken lambda probes causing these symptoms.

That would be lambda sensor fault causing rough idle

Thanks everyone. I'll have a dig around the Nanocom instrumentation and Motronic errors I think my lambdas were replaced. I remember insisting on Bosch. But that might have been my wife's car. It has a new (genuine) MAF because I'm planning a Tornado chip upgrade and they recommend replacement at 80k.

If you switch the ignition on, plug the Nano in, get it to the correct page then start the engine, you'll be able to look at the fuelling. You should be able to see whether it is in open or closed loop and what the outputs from the lambda sensors are. Not sure how it works with a Thor, but on a GEMS it shows OPEN or CL, lambda sensor voltage and short term trims.

Super! Thank you everyone.

this sounds like my intermittent (but getting more often) fault.... watching.