running too rich?

[manga_blue]

Personal experience with replacing the O2 sensor was that:

Before the change, the car ran rich, it was sooty inside the tailpipe, there was a nasty richish sort of smell in the garage or when you stopped with the wind behind, fuel consumption climbed from 8 to 10 l/100k, the idle had a few irregular bumps (sorta micro-backfires in the headers), the car felt mushy up to around 3000 rpm then OK above that.

After the change, it purrs at idle, tailpipe is back to dark grey, it pulls much more smoothly from ridiculously low revs (like 1200) in 4th and 5th, there's no noticeable difference in top end performance, I haven't checked fuel consumption because every tank since has had track work.

[GP]

Do you think that the 02 sensor should be replaced at periodic intervals?
My car runs a bit funny at an idle and has little power at low revs and burns more fuel than I would expect.