Was going nuts for a couple of days trying to track down a heavy cyl 3 misfire (at idle and beyond just feathering the throttle), unplugging plug wires at the distributor, swapping plugs and injectors around, checking fuel pressure, ignition part resistances, etc. All checked out. Everything by the book except doing a valve adjustment and an intake leak check (still going to do that soon).

I also installed a new cap, rotor, and plugs I had waiting for the next change. Helped with the misfire that was occurring under almost any kind acceleration, where anything but feathering the throttle would basically kill cyl 3 and cause the CEL to blink after a couple of seconds. It pushed the misfire back to moderate/heavy throttle, allowing me to drive the car with people behind me again. Also mostly calmed the blinking CEL inducing choppy idle.

Then I read about checking to see how the plug wires arc, by pulling them slowly off the spark plug with the car running. You should hear a fast clicking from each plug wire end arcing to the cylinder head as they get too far from the plug, and eventually, see the arcing at the end. If the insulator is broken anywhere, you'll clearly see the arc coming out the side instead. Best done at night or in a garage.

And that's exactly what I saw on cyl 3. As I pulled it off, I saw it arcing out the side of the insulator. Pulled it completely out after turning off the engine, and there was a very slight crack. Filled that in with a blob of silicone, and the car runs better than ever. New wires arrive tomorrow for a permanent fix, but silicone is a perfect temporary band aid. Drove the car for a couple of hours today without any misfiring. A method like this isn't shown in the repair manual, and my wires had resistance well within spec, so by the manual, they're supposed to be working fine, even though they're definitely damaged.