This sounds that the engine is running lean when the engine is cold.
With regards to the Ignition leads, there is no harm in doing a resistant test on them, but if you have a faulty lead that would also affect the performance when it's hot.
This problem when its cold, may be caused possibly by either of the following:
1)An air leak around where the inlet manifold to head joint gasket , this can be identified with a can of carb cleaner.
2) Check the small cluster of vacuum hoses to the right of the dipstick, as they have been known to split and also maf hose to throttle body joints for airleaks with carb cleaner
3) Ensure the lambda sensor is still tight as they have been known to work loose and suck air in if it has recently been removed.
4) Clogged injectors( run some injector cleaner concentrated through the tank with the fuel) or air leaks around the injector seals . (to identify if theses are ok, test with carb cleaner).