Engine problems, 01 2.2L sunfire

i dont knw if anyone can help but i recent bought a 2001 2.2l sunfire and it was fine, then one day i noticed when i idel the rpms wout drop from 600 to 500 for a split second and the car wou kind shake and then when i drive its smooth liek butter. so then when i was installing my cold air intake i saw a loose spark plug wire, that seemed to solve the issue for about 3 weeks then saturday night it started again... only when the defroster was on, it was on because when its off it rattles liek metal rubbing on metal.. ac clutch needs tgo be fixed.. but then sunday i went to go out and i as drivng down the road and i had no power at al, it sounded liek it was strggeling when i gave it power, i was goin thru the forms so i think it may either be the catalitic converter or the fuel filter, hopfully, cheap fix. but i pulled off a wire and found black stuff on the plug, what could it be? oil? possible the stuff u put on the plug to make a seal? i hope the warranty will cover it, and 1 more thing when i got it they replaced the air fuel mixture modulator cause it was spittin and puking, that may be it as well, any other ideas?

The power thing does kinda sound like your cat...but I don't know for sure

if u want to see if it is ur car try running the car in first gear all the way (u can do half way down) down ur street ande then see if it clears it u then drive it and see if it runs fine than it might be a plugged cat.

drive it first and see wut it feels like when it jerks(if it does) then do the first gear thing.

Thanks for the advise, i just took off my cold air inke, cause im taking it to the dealership firday, gotta love the warranty, and when i press on the gas it sounds liek it sputters, i think it may be the cat, but also mabye the air fuel mixer module, cause it smells liek its not gettin enough fuel, and so when it idels, it sounds as it it wants to stal.

Took the car in today, turns out a faulty wire goin to comuter was the culprate, it was sending false signals causeing it to misfire