I suspect that the device they are talking about is the cold enrichment thermostat. If it's lost its ompf it will definitely cause problems. The device is under the verticle tower at the back of the pump. It has two water hoses going to it. The thermostat is under the cover. If this is the device it is easy to test.
There is a airfilter at its base that filters the additional air that is also allowed under the cold conditions. Both activities are directly related to the length of the t/stat which of course changes with temperature. Remove the air filter and place your thump over the opening. At idle cold the act should stall the motor or severely reduce the speed. When fully warm the act should not drop the engine spedd even though a suction can still be felt. This range is critical and if full can be adjusted for final set-up, but a bad t/stat will be the same wam and cold. The piston in the housing right below the t/stat also freezes due to coolant leakage from above. The piston can be unfrozen and cleaned with emory paper.
Bosch Master, ASE Master, L1
33 years MB technician