[Schulisco]

If it's neither the ECU/DME or one of both flywheel sensors take the ignition coil also into concern. They die slowly due to heat and / or vibrations, mostly on CIS cars with the CDI as the coil is mounted on top of the cooling fan case. But I also have few credible reports from dying ignition coils on 3.2 Carreras too!
The behaviour of the car with some stalling issues may fit pretty well in this manner.

But also broken soldering points on the ECU board after decades of working can cause exactly the same behaviour.

In case of the coil the test is pretty easy: Get a replacement from any car with a single ignition coil with transistor igntition for testing purposesand see if the stalling engine persists...

Last but not least: Use the three wire bridge to rule out the DME relay as this may also fail causing a bad start and/or stalling issues:
https://forums.pelicanparts.com/porsche-911-technical-forum/1031064-84-carrera-non-starting.html#post10482778
https://dorkiphus.net/porsche/showthread.php?t=16859

Thomas