[tirwin]

So you have SSIs and the CIS O2 sensor? Where is the O2 sensor bung located?

Obviously you’re way lean if your AFR is 16. The car is trying to tell you something. It is leaning out. It probably got to the point where the O2 can’t correct it. You disconnected the O2 so it went to fixed 50% duty cycle. Bandaid. It will get worse and next you’ll have a lean backfire.

First thought is you have unmetered air getting in somewhere. If you let the car warm up and idle in the driveway, take the oil filler cap off. If the rpms don’t change you have a significant vac leak. You’ll need to track it down. Smoke test or carb cleaner/unlit propane around the usual suspects method.