IfI tune out the O2 sensors will I be running an open loop and get terrible gas mileage? Also since my car is catless, if I tune out the O2's can I still pass inspection?

 

You never want to tune out the O2 sensors that sit in front of the cats, those are the ones that control your mixture. The after cat O2 sensors can be tuned out without any issues, but without cats you won't pass emissions, especially if you have a visual inspection like they do here. If you don't tune out the after cat O2 sensors they definitely won't let you pass because your SES light will be lit and a car cannot pass if it is.