Hi Massive,
944 Progressively Worse Idle...(weaker)
My worse idle was rotted hose to the "Y" connector- PART 7
Check hose connections under the intake. Tighten hose clamps. Check for rotted hose.
I do not think it is the ICV-idle control valve, throttle valve or MAF, but all are possible.
Next (IF NECESSARY)----remove the intake, new seals and more hoses to check
Go to Porsche Classic parts catalog for more pictures:
https://www.porsche.com/usa/accessoriesandservices/classic/genuineparts/originalpartscatalogue/
Just a few possibilities. GL
John