Hey Mark,

I just wrote a story for a technical pub on this very topic. The tech I interviewed said that he was seeing lots of random misfires and this very DTC. He solved it on many cars by doing an injector cleaning. Here's what he does:

Mix ~ a half-pint of engine cleaner with about a quart of the appropriate octane gasoline in the injector cleaner and attach it the fuel rail. Running engine cleaner through the fuel injectors also cleans any carbon deposits off the intake valves.

For the second part of the engine-cleaning service, there's a special nozzle for the cleaner that attaches to the air intake duct in front of the throttle body. This cleans it, the throttle plate, and the idle air control motor.

For the third part of the service, add a bottle of the injector cleaner to the fuel tank and top off the tank with gasoline, to mix the cleaner and gasoline thoroughly. Reset the check engine light, and the vehicle is good to go.

Hope this is of use!

Kirk
1992 500E
69K miles
Pearl black/grey

Just to follow up on these posts:

Replaced O2 sensor between engine & catalytic converter. Reset check engine light. Has worked for several months now without coming back on.

So - final tally:

Leaky injector o-rings, which masked faulty O2 sensor.

Plus a lot of other things that were probably OK, including MAF.