If it is unplugged will it effect performance on a flashed ECU?

I was informed that the front is the more important of the two, and the car will throw a CEL but it will not effect performance. The rear is really only for emissions purposes. Is that true?

 

i think you are correct. front is for air/fuel, rear is for catalyst efficiency. im not sure.

 

Thanks.

 

Anyone else? I have noticed that the car stumbles and stalls when it is first started. I have 264's and a flash. It seems like it takes a second for the closed loop feedback to kick in or something b/c after it catches(idle) it is fine, kind of wierd.? I don't think it is b/c of the rear O2 sensor, but maybe.