Like the title says, do I need the primary o2 sensor. I have a wideband attached to the my downpipe and have taken out the primary and secondary o2 sensors. Do I need to put the primary one back in?

 

No you do not. I have mine disabled in Flashpro, because it took a shit on me after only 1,500 miles and this was a new oem replacement. Just make sure partial throttle is tuned somewhat close to 14.7 afr as the computer will not adjust it any longer and you will be fine.

 

So is it better to run with or without the primary o2 sensor on the flashpro?

 

If you have a wideband you can run the car without the primary O2. The factory O2 will only adjust light load fuel tables, so it is only really a fail-safe. But it will only do this if you have the factory O2 sensor enabled and installed. I think that my car runs better in partial throttle with it disabled but my cars partial throttle is also tuned very close to 14.7 afr.