Oxygen Sensor and CIS tuning
 

I know this has been brought up a few time before but can't find my particular problem. I recently brought my car in to have a valve adjustment performed and to fix some oil leaks. I had been chasing the leaks for a while and got fed up with them. Now to the question. I had the mechanic check the CO level and adjust if necessary. With the oxygen sensor disconnected he adjusted the level to .6%. When he reconnected the sensor the CO level jumped to 1.2%. Is this normal?? I was thinking of replacing the sensor and taking it back to readjust the mixture. The sensor probably has around 20,000 miles on it. I know there are a lot of you that disconnect the sensor completely and adjust the mixture to about 3-3.5%, so should I just disconnect the sensor and drive the car or replace the sensor and have it readjusted? BTW the car is an 83 SC with no CAT and SSI's.

Thanks,
Pete
83 911SC

I thought what is supposed to happen is with the O2 sensor disconnected you set the CO to 3% then hook up the O2 sensor and the CO should drop to .5%