Lesson learned - check those boots!
 

I've been chasing a misfire in my 1998 S320. At first it was intermittent. Then it began to start missing as soon as I got on the accelerator pretty good. When first started, it ran fine as long as I kept my foot out of it. But when I accelerated to get going with traffic it would throw a CEL and a code P0301. If you shut the car off, the process would repeat.

I really thought it was a coil failing or possibly clogged fuel filter. So I tried both of those things with no luck. Today I happened to notice a smudge of white dielectric grease on the outside of the boot for #1. Looking closer you could see a tiny hole. Apparently the grease was blown out the hole by the spark. I swapped the boots between #1 and #3, cleared codes and retested. Same behavior, but the code followed the boot to #3.

Local AZ had Bosch wires for it. Threw those on it and problem is solved. I still don't understand why the problem only occurred after I put a load on the engine, and did not go away until it was shut off. But whatever, it's fixed.