I am getting my oxygen sensor replaced today and the mechanic gave the car back so I could do errands while the part is being delivered, which will take several hours. In the meantime, the car's oxygen sensor has been removed.
I notice that the car engine is a lot more noisy and when I accelerate, it sounds like a chainsaw.
Is this just because the oxygen sensor has been removed so there is hole in the cat emitting noise, or is the engine making a fundamentally different noise due to different running behavior?
What effect on the mixture or other engine management parameters will driving without the oxygen sensor cause?
Note that this was the post-cat sensor.