All -

I've been chasing down the driveability gremlins on my 1993 300E. I now need to replace the O2 sensor - car still has the original sensor after 13 years/110K miles.

Any tips on how to get that puppy out of there? I soaked the threads with penetrating oil a few days ago. Access to the O2S isn't exactly great. Is it worth dropping the exhaust system to make more room? What kind of tool is the best to use?

To recap, I'm chasing the usual driveability issues on an HFM-SFI 104 engine. So far I've replaced the plugs/wires/coil connectors to remedy a misfire problem. Pulled codes and determined I had a dead MAF - the computer was in "guess the mixture" mode. Replaced MAF and I'm now free of error codes and car drives fine. Still have a bit of an idle oscillation - it'll go up and down perhaps 100 RPM when rolling to a stop. After ~5 seconds it settles down to a smooth idle.

Many of the usual suspects were replaced under Starmark in the last few years: engine wiring harness, fuel pressure regulator, OVP relay. Car still has the original coils and EA/CC throttle actuator.

I can't find any vacuum leaks; will look again tonight.

The EGR valve is dead, won't hold vacuum. I've got the line to it capped for now. So long as the EGR valve isn't stuck open, I shouldn't have any idle issues from it, correct?

Current plan is to replace the O2 sensor, run some fuel injection cleaner through it, clean the throttle plate (I've read they stick due to accumulated oil vapors from the crankcase ventilation), and check further for vacuum leaks. If that doesn't fix it I may try an exorcism.

- JimY