No controllers, no electricity. The only thing electrical to the operation of the CIS (K-Jetronic) fuel system is the fuel pump. The warm-up regulator and the cold start valve also have electrical connections but they do no have a function to the warm motor.
The cold start valve sprays extra fuel ONLY DURING CRANKING!!! for a length of time up to 12 seconds depending on the engine temperature (thermal time switch in cooling system). The electrical on the warm-up pressure regulator is to heat up a bi metallic inside the device so that the pressure drops faster than the time it would take for the heat of the engine to do it. If the electrical is off, the enine will stay on the enrichened state much longer than necessary. Once the motor is hot the device stays at the higher warm pressure even if the engine has been shut down for some time. Cold starting mixtures are not needed at those times and the heat of the engine keeps it that way.
There is absolutely nothing that can be diagnsosed on this system without pressure gauges. On your car basic mixture can be adjusted with an exhaust gas analyser, but if it is wrong at any other time like cold runnning, high speed running, full load running, etc. diagnosis will require a gauge. Setting up and verifying pressures are necessary.
In all engines the speed is determined by the air not the fuel. In the case where you openned the vacuum line and the engine speed increased, the engine had enough fuel to go with that air and the engine did what all engines do it went faster. On the other engine adding air must have caused the mixture to be so lean that poor running overcame the increase in engine speed and the engine slowed At any given airflow the engine speed will be maximum with the proper amount of fuel; too much or too little will cause a drop in speed.
If your observation was done to a warm motor there also is the possibility that one engine liked the enrichment that would come from the removing of the vacuum line and the other didn't. When the vacuum is reduced as in full throttle the warm-up pressure (control pressure in this case) goes down for full load enrichment.
Bosch Master, ASE Master, L1
33 years MB technician