My 89 XJ Renix has been eating up gas and its costing a lot. Recently, the jeep dealer replaced my O2 sensor for free due to a recall. The next day i replaced JUST the FRONT LEFT brake pads. I dont know exact numbers, but i know im getting low mpgs. My catalytic converter rattles terribly, it needs to be replaced, however it never had a bad effect. Could the o2 sensor have affected this? Maybe my pads are dragging? Anyone have either experience?

Also my RPM's used to slowly go done when letting my foot off the accelerator, however now it quickly DROPS to like 1200 rpms, why and could this be the problem?

Thanks

Never install brakes on just one corner, it's dangerous. Brakes come in pairs for a reason. You need to replace your catalytic converter.

Agreed. Do the brakes on the other side too.

As for your drop in RPMs, how fast are you going and what gear are you in when this happens? Without that info, I'd say the new o2 sensor is finally working how it is supposed to, cause that sounds pretty normal to me. A fouled up o2 can cause a high idle.

The renix era brake pads have specially nuts holding them in that has been stripped badly on the right. I dont know whats wrong!