I've got CIS on my 911 still and was having some trouble getting the idle set. I borrowed a friend's Gunson Gastester and got it set at the correct CO level but still had a few drivability issues. I eventually installed a wideband AFR gauge which proved very helpful in diagnosing problems as I drove the car around. It's also useful for setting idle CO level if you have access to this chart:
https://www.mgexp.com/article/co-to-air-fuel-ratio-afr-table.149