Make sure that you adjust the ignition timing as specified for your engine. You got an 1982 SC IIRC ... RoW or US model?
I own a 1981 US spec SC with WebCam 20/21 camshafts which is somehow comparable to the 964 cams...I use an programmable 123ignition and adjusted the ignition advance curve as the Porsche workshop manual specified, even with 5° advance on lower than 500rpms amd 0° advance around 1200rpm to make engine start easier.
See more on AndrewColognes page to the 930/16 engine:
https://nineelevenheaven.wordpress.com/maintenance-of-the-distributor/
Porsche Workshop Manual:
https://www.turbosition.com/_files/documents/Porsche_911_Workshop_Manual_1972-1981_EN.pdf

This is my car on startup, sat for some days, did mot ran for some days, about 15°C ambient temp.

https://youtu.be/ynJhhmi4TCM

Thomas