the plugs should last hell of a lot longer than 7k, if the electrode gap on the plugs were to big it will not start, but if it is only too big on 1 then it will misfire like a pig, that not the problem though, personally i think it is an electrical problem, such as a relay, i would check them first as the engine management relay could be faulty therefore when starting on cold the ecu isn't telling the injectors to inject more fuel for cold starting.
