The cold start valve which is the sort of fifth injector should only open for between 4 and 15 secs approximately so effectively should have little or no influence on cold performance of the engine. Do the obvious first, remove the banjo shaped rubber duct and check that the metering plate is corerctly centred in the plenum chamber. If it drags then the richness of the mixture will be affected. If it needs re-centring this is easily done with a .004" feeler gauge tested at three points around the plate. Failing this then I am inclined to think that you have a problem with the warm up regulator, aka control pressure regulator. What this this seemingly inert block of aluminium on the inlet manifold (iirc) is supposed to do is lower the control pressure in the metering unit. The control pressure controls how much the air-flow plate deflects for a given flow rate, so for example when the engine is cold the arm will move further up to reach the stable position in the airstream for a given airflow, which in turn moves the metering spool further up, opening up more of the metering port to fuel flow, long story short acting like an automatic choke. Inside the control pressure regulator is nothing more than the open ends of the feed pipe from the top of the metering head and the return to tank pipe (whch may or may not "t" into the main return pipe I can't remember) and a heated bimetalic strip with a seal on it that when cold bends back and allows the two pipes to interconnect, reducing the pressure on one side of the stainless steel diaphraghm in the metering head. This is what allows the round air-flow plate to deflect more, richening the mixture, when cold. As the metalic strip heats up, (electrically and via heat soak) the inter-connection between to two pipes gradually reduces until, once at the corect operating temperature, the two ends of the pipe are sealed from each other and the increase in control pressure pushes back against the forece of the metering plate more and leans the mixture out. A control pressure regulator will be considerably more than £40 probably by an order of magnitude. It would certainly be worth, in this day and age, and the vintage of the design, taking off the cpr and taking it apart to see if the strip is opening up properly. Conversely the rubber seal may have deteriorated giving false richness, which someone may have attempted to compensate for by leaning off the mixture via the adjusting screw on the metering head. I say this so that if you find the internal seal is useless and repair it even temporarily you may have to tinker with the mixture via the screw to rectify the rectification if you see what I mean. You might want to smarten up your by-pass into something more permanent because the 2.0 engine is infamous for its warm start problems, caused by a vapour lock. This happens when the check valve on the end of the fuel pump lets by. For brief stops the fuel accumulator will maintain pressure but will not keep the pressure up for more than a few minutes. I know this from experience with a jury rigged earth bypass for the cold start valve which I used to use to start the car when it was warm. The fuel pump relay has a safety circuit in it so it will not run until the it either has the earth return on the metering body broken by the plate lifting on early models, or by the fuel pump relay getting pulses from terminal one on the coil on later models, so at 10v (starter engaged) the fuel pump has what is known as "bu99er all chance" of pressurising the fuel lines. Then the fuel pump packed up and the only connection I could undo was the check-valve to pipe connection so when new pump was fitted complete with new check-valve the warm start problem dissapeared.
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