Why is my car running rough after my spark plug an wire change?

Yes the terminal end on the spark plug wire is a must for a good connection.Other wise the spark has to jump from the wire core to the terminal.Also a cracked plug is going to cause a problem.What are the exact code numbers you have?

i would recommend first check for correct spark plug gap,then make sure that you didn't disconnect a vacuum line by accident

okaybouquet, did you get this figured out? Did you replace the plug leads incorrectly, or was it the broken plug?

well okboquet....an numer of things i need answers to so we can solve your issue first did you buy the correct spark plugs,most newer GM vehicles use irridium plugs whitch come pre gapped from the mfg. so if you tried to gap them they might be damaged,second did you disconnect the neg terminal from the battery,if you did did you wait a few minutes for your PCM to relearn its parameters? if you did not it will cause the engine to run rough for a couple of complete engine cycles,Could be what the other readers have described,a cracked plug would cause this,so would mis connected spark plug leads but i'm not sure that would be it because the wires on todays v-8 engines are interchangeable,please describe "running rough" only at idle or all the time?is it surging,the it would be a vacume line sorry okboquet i've most likley made matters worse.just trying to help im not nearly as skilled as some on here that can answer car problems.with very little to go by,but hey atleast you trying good luck

I think he's forgotten about us. He hasn't replied since August.