Im pretty sure you cant smell carbon monoxide
JK
If you adjust the timing with the engine running, the computer is going to keep it where it wants. Thats why on the TPI cars you have to disconnect the wire that controls it. If the computer is cutting the timing at idle, it will prob make a code. I know the TPIs cut timing when they dont detect a knock signal. Im not 100% familiar with the lt1 yet as it hasnt broken down on me 15 times like the tpi formy. But the car runs correct? if so, what is it doing exactly? and if you can read the timing off the ecm why cant you read the o2s?