[Roby466]

Hi,
I was always trying to have my 81 911sc to run correctly and was never able to get good idle, good acceleration and smooth driving all at the same time until I fixed the timing and mixture properly.
I replaced the distributor because the other one was not advancing properly. If yours is ok, then you save 1500$.
I set the timing at 5 degrees BTDC at idle with both advance and retard hoses disconnected and plugged (golf T). I then plugged everything back in except for the ox sensor.
Make sure your relay works well under the passenger seat and that your fuel pump relay has good connections (ask me how I know)
Make sure the car is at operating temperature and put a voltmeter on the ox sensor lead and ground and check for the voltage output to oscillate around 4.5volts at a 900 rpm idle (that will give you proper mixture at idle without needing a gas analyser).
Once this is done, plug it back in and set the idle speed again if it moved. That gave me perfectly smooth acceleration and modern car like driveability around town. No more flat spots, no more hesitations under light throttle at lower rpm, a smooth running engine.
If your ox sensor is old replace it. If it is fairly new but the car has been running rich for a while, you might have to reset your mixture after a bit of driving as running it leaner now will clean it a bit.
Good luck and it is worth to plug that ox sensor back. Older cars were supposed to run without it and had a few more CIS components to adjust for partial throttle, the 81-83 CIS should run with the ox sensor plugged. Better driveability and better gas mileage.