This applies to Bosch K-jet only, Control pressure is what “controls” the mixture (rich when cold, lean when warm) this is done by applying pressure to the top of the piston in the center of the fuel distributor. A low pressure allows the piston to move higher in the fuel distributor to provide more fuel for a given air flow. Increasing the pressure forces the piston lower for a leaner mixture for the same air flow. Control pressure needs to be checked cold, and warm. The two wire plug on the warm-up regulator heats the warm-up regulator to lean the mixture early before the engine is completely warm. This is done mostly for emissions regulations. Disconnect this plug for cold testing. While the engine is cold open the valve on the continuous injection system CIS gauge and you will read cold control pressure. Cold control pressure will vary according to temperature. Example, at 10 degrees Celsius you may read 1 to 1.5 bar, at 20 degrees Celsius you may read 1.8 to 2.3 bar. Reconnect the plug to the warm-up regulator and the control pressure should increase over the next few minutes until you reach warm control pressure, usually 3.4 to 3.8 bar. If the car is equipped with acceleration enrichment by means of a vacuum line connected to the top of the warm-up regulator, disconnect it and control pressure should drop 1 to 1.3 bar. These pressure values are approximate and actual pressure values need to be obtained from the manufacturer or Bosch.