update: I think it was an issue with my IAC. When I rebuilt the top end, I accidentally routed a wire bundle too close to the accessory belt and it sawed through a solid blue wire, which I was told was for the IAC. Like a dummy, I took my sweet time repairing it. I finally pig tailed a repair wire there, and it seems to have fixed it for now. I really need to solder it and put in some heat shrink butt splice connectors, but clearance there is pretty tight and I don't think I can get a conventional set of crimpers in there.