As jp said, engine speed is a air flow problem not a fuel quantity issue.
Forget the term warm-up regulator. Use the term control pressure regulator and you will stay out of trouble here. It keeps one from assigning functions by leaving the interpretation out of the name. In your symptoms the car is already "warmed-up" and the control pressure regulator has the smallest affect on a warm car.
My initial reaction was a vapor lock condition caused by the loss of residual fuel pressure. The condition of high idle speed changes that concept. With that thrown in I think you have a variable vacuum leak. Large enough to impede lean restarts, high enough to raise the rpms. One part that the euro car has that can cause this is a decel dump valve. It is a black plastic valve bigger than a golf ball and hooked to two large rubber pipes and a small vacuum line. It is below, outside and to the front of the airfilter. During throttle closed decel the vacuum line causes the valve to open and large volumes of air dilute the mixture.
Bosch Master, ASE Master, L1
33 years MB technician