[ImperialCrown]

The typical injector failure will make it run rich and you may see large drops falling onto the throttle blade as it idles. The throttle position sensor can also fail without leaving behind a code. A leaky EGR (if equipped), can also make for a rough idle quality.

 

[ImperialCrown]

Does this seem to happen warm or cold or does it make no difference? If the idle fluctuation and stall happened within the first minute or two after a cold start, the O2 sensor would not be active yet.