Annoying cold start problem on a 1997 2.5 Boxster

[Retroman1969]

This is probably irrelevant since it sounds like you have been dealing with it for awhile, but my 1999 Boxster had those exact same symptoms and also didn’t throw any codes. Turned out to be bad gas.
Once I flushed the tank out and filled up at a different place, it went back to normal immediately. Symptoms never returned.
Second guess would be the temp sensor. Wouldn’t be out of the question that the MAF sensor could be faulty even though you’ve replaced it.

[poortmanc]

Looks like it was the throttle position sensor (TPS) which was giving wrong values on the first percentages of throttle in combination with a loose AOS hose on the bottom.

This explains why after every reset the car ran more or less fine (default settings) - and became worse the more kilometers I made.

Idle hunts still a little bit on a cold start, but not stalling any more (hunting between 700-1100 RPM and quickly settling). Fuel trim on the long term is still a bit off, but becoming better the more I drive.

Bank 1 Long Term: -1.6%
Bank 2 Long Term: -4% (seems like something is not yet correct here)

I'll keep you posted,

Happy holidays.