New-to-me SR5 with 240k on it. Trying to get it ship shape.

Did timing belt etc and LBJ's.

It's thrown a CEL twice now. First time was shortly after I got it and it had been sitting a while, P303 misfire IIRC, though it wasn't hesitating and ran fine, and the CEL cleared on its own the next day. I figured it was an injector that was just waking up after sitting for a while.

Two weeks later (it was sitting for that time since I was saving up for the timing belt and LBJ's and didn't want it to have an issue in that time) I got everything done and was noticing some low idle issues at a stop. Would do it in neutral or in gear, low struggling 600ish idle but no CEL for that.

SO....I tossed some SeaFoam high mileage fuel treatment and a full tank of 91 octane, hoping that would address my idle issue as it seems to have for some other folks. Instead, I got a CEL within the first 5 min of driving it. I tightened the gas cap in case *that* was the issue but no dice.

I'm hoping the full tank of fuel treatment will do its job and address this but wondering if anyone else has had any sort of issues running 91 octane? I can't think of a technical reason as to why that would throw a code, but thought I'd ask.

Doing plugs and plug wires next.