The "warm up valve " or fuel pressure regulator ,the squarish unit mounted to the top of the thermostat housing -- it has two fuel lines , an electrical connector and a vacuum fitting . This pressure regulator is what determines the lean or rich condition for warm up cold start and normal running . To properly check this CIS system you need two fuel pressure gauges to measure the system pressure and the control pressure . 

The control pressure cold 20 degree C with engine stopped fuel pump running  1.1 bar +,- .2 bar --cold  running with vacuum it should be 1.6 +,-.2 bar . The control pressure warm engine stopped , fuel pump running 3.0 +,- .2 bar -- warm engine at idle 3.6 bar +,- .2 bar . The system pressure at the fuel distributor 5.2 to 5.8 bar . This warm-up regulator directs the fuel distributor to add more fuel when the engine is cold it has an internal bimetallic electric "spring" which changes shape as it is heated adjusting the pressure to lean out the mixture as the engine gets warm . This is a very simplified discussion of how the CIS system uses fuel pressure to adjust the mixture for various conditions .

Jim Bailey
928 International