Unplugging the sensor causes the frequency valve to stick open. This allows the fuel distributor to do its job uninhibited. The frequency valve leans out the mixture by lowering the fuel pressure when the O2 sensor detects emissions out of its range. I took mine out when I added SSI's and replaced the hole with a plug. My car passed emissions testing without the sensor, back when I still had the cat on. Doing this is also supposed to make the car run cooler, but I'm not sure if this is really apprecible or not.
You will need to have your mixture reset with an EGA after you unplug the sensor. After that, smooth sailing. But as you said, make sure all other potential causes of idle problems are also looked into as well.
Good Luck.
Nick.
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Nick Shumaker
1982 911SC Coupe
nickshu@yahoo.com