The cold start valve is controlled by what is called a "thermo time switch". It operates only when temp. is below 59degF and has no effect on the idle speed itself.
The cold start valve is only opened for a few seconds (about 20sec. at -20C) after the engine has started.
So, if your car starts OK, but fails to idle, the problem is very unlikely caused by your cold start valve or the switch triggering it.
Look for vacuum leaks, idle control valve, bad spark plugs, distributor cap, rotor or spark plug wires.
A partially clogged fuel filter or low fuel pump pressure could also be the culprit.