While there was absolutely no data provided on why the plugs would improve the situation except that Japanese NGKs "NEVER" work in German cars, and that it'll just work... I swapped plugs and wires with my friend's 300E anyway. He has the H9DCOs. We both have the OEM Bosch wires, mine were somewhat newer than his.

And it solved nothing at all. Problem persisted on my car, and his car drove no differently either. It's not the plugs, or wires. Period.

I sprayed some carb cleaner around the injector seals and idle changed just a bit when I hit cylinder 4, but not that much to make me immediately think it was a leak. I'll run a couple more tests to see what else it might be. Holding the pedal halfway down while starting the car though makes it start really quickly, like 1-2 cranks, which would suggest fuel leaking into the cylinders when the car is off...