Interesting observation
 

I have a new to me 2001 Boxster. I just had the AOS replaced because of a surging idle when warm and excessive vacuum at oil filler. I didn't want to risk driving it like that. After the new part was installed, the idle smoothed out a little, but did not fully resolve.

Then, a week later I went to the dealer to get a new key programmed. Now my idle is rock solid at all temperatures. Either the reprogram cleared out some fault code or they accidentally fixed a vacuum leak while poking around the car.

They spent some time looking for things they wanted me to pay them to fix. Maybe they fixed a problem by accident while looking for others?

Either way I guess I am lucky.