Me to be lean on the passenger side of the motor and rich on the drivers side?

I changed my plugs out last night because my 97 had been stumbling lately and thought that may be the cause. Well all four driver side plugs were rich, so rich infact that you could still smell the fuel on them and the car had not been driven all day. The passenger side looked like they have hardly even fired, dry as a bone with no build up on them. A couple still looked pretty new. The plugs have been in for maybe 1k miles.

The stumble is still there at low RPM's but not nearly as bad, I can just barely feel it now.

It's a 97 auto and the only mods are Pacesetters LT's, 3" x-pipe w/ bullet mufflers.

 

Misfires, an exhaust leak before the O2 sensor, or a faulty O2 sensor on the rich side could be causing the problem.

 

I had a Problem similiar before where 1 side of the motor was missing (could tell b/c the plugs were back, fouled them out)

Change the 02 sensor in the exhaust on that side.

 

In this instance a scanner and inpection of your exh system would really help, after inspecting the exhaust system for leaks BEFORE the O2 sensors.

The scanner then would tell you your short and long term BLMs and the actual readings from the O2 sensors. If one O2 sensor acts sluggish or unresponsive then the O2 would be more than likely the culprit.

I allways like to change my O2 sensors about every other plug change. I have been bitten by them a couple of times. I have even had one short out on me and blow fuses !!