Yet another post! Weird idle, stuttering, sooty pipes oh my!, Weird stuff is going on, would love some help! Options

[CoolGuyArik]

Hello again! I'm loving the forum! It's been a big help to me and the car I love!

I've had this weird idle problem for a while, about a month. I can't pinpoint it ecactly, but one day, after putting in lesser grade gas, my car ran like crap. Misfiring, sputtering out, the works. I replaced my entire distributor, my sparkplugs, and the wires, and since the distributor, it can idle. Now though, I have these intermittent drops in idle, like a misfire, but only just. And my timing is advanced all the way, because anything lower gets the idle to 500ish, and spots of soot spatters the driveway. Alongside the low idle, blipping the throttle with the timing in the middle makes it stutter, then start increasing in revs.

My upstream o2 sensor works, since I tested it with a multi, but unplugging it fromits harness gives no CEL and no codes, and nothing changes. The downstream doesn't give any codes either if its unplugged. The fuel system seems fine, because it doesn't get starved at high rpms. I've changed the fuel filter.

I'm just looking to see what it is, or see if someone else has had this happen. I'd love to get my 6gc mechanically in top shape for the school year. If you need any other info, just put down a reply. Thank you!