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.

5vz doesn't care about octane below 87, no good comes from anything higher on this engine.

You need to clean the MAF and IAC.

Guessing you replaced plugs and wires already?

Clean the throttle body too while you're in there cleaning the iac.

UPDATE: Ha. Turns out later today, it got significantly worse. Rough idle, missing, flashing CEL and just struggling to get down the road. Yikes.

Was planning to replace the plugs/wires today anyway, and when I did I found one plug had some extra material on it....the metal end of the plug wire was broke off completely and stuck on the plug (and not easy to get out). This was with factory plug wires of unknown age...old enough that the plastic clips cracked upon removal.

The CEL is still on but it's no longer flashing, need to pull that code today but I suspect it's left over from running on 5 cylinders for a moment.

Cleaning the IAC, MAF and everything next just because that seems smart.

Thanks for confirming the 91 octane fill up wasn't an issue, nor at all useful, I'll save that $ in the future.

You probably know this yet the flashing cel is the ECU way of trying to tell the drive to let off the throttle because way too much unburnt fuel it making its way to the cat which if left unchanged would probably ruin it, more troubles.

Cleaning maf, iac should take care of most of the issues but as HiLife said, will also help.

Take it easy on it until you get all this done. Luck.

If you plug wires were that old I wonder how worn the spark plugs are.

Regular copper plugs have around .001” of gap erosion every two months.


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They were worn, for sure. None of them LOOKED gross but probably were.