Just a guess says that you are experiencing injector leakdown or fuel vapor lock (which would be caused by fuel pressure leakdown). Actually on second thought, probably just the vapor locking condition because if an injector or two were leaking down they would stay leaked down over night and you would have misfire till they pumped up all the time.
The reason this causes your idle symptoms would go like this: When cold, no vapor lock, car performs properly. When started after hot soak the car runs poorly due to poor fuel control with vapors in the injector and line (due to lack of residual fuel pressure - fuel boils at much higher temp when under pressure). Due to the fact that the engine is running poorly the idle control goes maximum open to try and maintain speed. The vapor locking usually clears after 15-20 secs and when it does the engine instantly runs right and at the higher rpm due to the valve being open. In a second or two the thing realizes its too fast and regains control and the event is over.
Bosch Master, ASE Master, L1
33 years MB technician