Interesting failure mode.

—^ And check the housings for cracks.

I ran into that once two decades ago: dropped a cap on the shop floor. Didn’t think anything of it at the time. The 928 went straight to limp mode. Wasted a lot of time finding that.

I’m reminded of another ‘funny’ problem. Intermittent misfire. Plug wires had been replaced by ‘someone else.’

Yup, Used the wrong coil wires. Of course, you know why there are four coil wires in a set.

How long did it take previously to start missing, you said recently it takes 30mins?

Assuming the coils, leads and distribution caps are all fitted properly and functioning I would say don’t let the LH work become a red herring. It needed done to eliminate it and provide future reliability but the fact it is still running rough at part throttle and only once warmed up, in my mind eliminate electrics and injectors. I refer to my original reply (post 2 or 3) and say you have a small air leak into the manifold which becomes more apparent once the fuelling drops after warm up.

When you accelerate it goes away because the LH adds more fuel and it is not as detectable at warm up as the LH is adding more fuel as standard.

I had the same symptoms when the sealant provided by Carl (928 MS) failed on my intake manifold spacers. Small air passages formed through the sealant resulting in a lean running condition providing the same symptoms you are describing.

I diagnosed the problem and source quickly and replaced the sealant for something more suited to the job. My problem is fixed and the car has been running fine since.