I've got an '01 Tundra access cab V-8. A while back my passenger side catalytic converter was stolen. I drove the truck for about a week like that until I had the part to fix it. I used an aftermarket bolt in catalytic converter. I left the stock catalytic converter on the driver side of the vehicle. There didn't seem to be a problem with the O2 sensor so I didn't mess with it just bolted it in. When I reinstalled the cat the truck was running pretty rough and it was in an irregular fashion. It was pretty lumpy. So I unplugged the battery overnight and drove the truck for a good hour on the highway the next day to reset the computer. The truck runs smoother than it did. Now it is closer to a regular rough idle as opposed to a really lumpy rough idle. Does anyone know what the problem could be?