your missing a trick here jimbo its ok cleaning plugs but plugs dont really clean back in the day when they got lumps of carbon on them we used to sand blast them from them bottom up inside they loose there resistance condensation kills them from inside and outside the engine if its fireing on all plugs and the spark isnt yellow and should be a darkish blue colour if there blue a new coil isnt going to do much. what ive over looked is the idle control valve this does the cold start mainly pull it out and clean the housing that it goes into theres an o ring on the bottom of the icv they become stuck clean the houing with a bit of 240 wet an dry and wd40 if the o ring is stuck it will stop the icv from operating which might not give you cold start dont waist your money on ht leads all the leads dont go down at the same time you might get the odd missfire on one cylinder but to prove the odd missfire you can try moving the miss to another cylinder