Basically Porsche are saying they couldn,t find anything wrong with the CPS ( crank sensor ) .. the trouble is unless the car was running badly when they checked then theres no way of saying its ok .
I expect they tryed every way you described to get the car to run rough but it didnt hence they wouldn,t be able to find a faulty component .
Spacer refers to the correct gap between the sensor and the flywheel .. its about the magnetic strength generated by the flywheel teeth and the sensor .. too big a gap and you get a weak signal .
Its also a fix for a 996 turbo rev flair problem .. you fit a spacer .. didnt really work on that problem though but i digress
If the car runs fine then there is no problem to find and it doesnt matter what you test it will all test as ok.
Trust me faults like this are every mechanics nightmare .. ive had many over the years and have had to be honest with customers and just say drive it and see how it goes .. if it returns or becomes a constant problem then we can find it .
This is were fault codes help .. even if the fault isnt there it still gives us an indication of where to look and then make an educated guess .
MAF sensor .. always possible but i feel the PSM light / Maf load signal was corrupt due to just how bad it was running at that point ..
Mafs tend to be contaminated .. basically they give a false reading .. this will give an incorrect fueling but not Imho the type of fault the Op has .
Its more a constant thing with mafs .. granted the signal could drop out at the temps the fault occurs but a fault code would be generated and so far we have no codes to work on .
The PSM doesn,t care how bad the engine is running it just wants a signal which in this case would have been all over the place.
Its given up and said sod this im off down the beach untill you can give me something i can work with .. hence its shut down and taken the day off!
991 tend to be very good at generateing a code for even the smallest of deviations so a lack of codes means everything that can be tested by the car at that point is with in specs ... although it might be out of range at a given parameter.
Hence all my answers have been based on what i think could fail at high temps but not generate a fault code .