Could it be a bad O2 sensor ?

[orph]

Here is the situation:

1986 930

Earlier this Summer, had some seals replaced, new clutch, etc. In the process of doing the work, the settings associated with the O2 sensor we adjusted to specs.

For the next few months, the car would no longer idle like it should following a cold start, even though it had before. Start was immediate, but within a few moments, the car 's idle would drop off to 400-500 RPM and barely run. Once warm, idle was back to normal.

During the last month or so, not only do we have the low idle issue, but also black exhaust smoke for a good 3-5 minutes, plus even mild acceleration results in the car starts boughing down. But, after a few minutes of driving, the car runs fine, be it crusie, idle, or hard acceleration.

Might all of this be associated with an O2 sensor going bad, or might I have issues with the WUR, or ???