That's annoying. At least they're supposed to be replaced so you won't need to worry about them for a while. Were the sooty spark plugs contained to a couple of cylinders or a bank? Was there a noticeable variation in how sooty all of them were? You had any engine lights come up?
On the loom side I would start by looking at your injector and coil plugs and make sure they're on properly and in good condition (give them a decent wiggle and pull to check if they're cracked and that they stay on correctly), then follow the loom back and start looking for cuts or where the wiring may have rubbed through.
While it's suuuuper unlikely, also take a look at the fuel pressure regulator. Generally they don't break, but make sure all the vacuum hoses are in place properly. In fact, go around the manifold and intake and make sure all vacuum hoses are accounted for.
Also found this thread while looking for idle air control sensor symptoms -
https://forums.justcommodores.com.au/threads/ls1-running-rough-and-surging.226481/