erratic running (rich?)

[Alan Pritchard]

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The good old 90q cis III is behaving very oddly, a few weeks ago it started
to drive really badly.... Absolutely gutless until around 4k and then it
would absolutely fly, it stunk of petrol so I did a temp fix of leaning the
mixture up a tad, which improved things almost to how it use to be, at the
time I suspected it to be the o2 sensor, I have always suspected it of being
on its way out. But know the car idles low when warm (400 revs) and when sat
on the clutch the revs surge upto 1200 and back, driving seems reasonable
with a few "flat spots"  but when changing gear and reapplying the throttle
the car lurches. This could be due to a dodgy idle switch which is on my to
do list. Any opinions gratefully received.