koon'sXJ

Well to start, I am new to the forum and after reading alot of others, am proud to be a part of this one.

Now for my problem....96 XJ 4.0, after driving a bit and it warms up, it will idle rough and try to stall, but clears out when gas is aplied. It is also running rich, I can smell it. I did a full tune up and the plugs had alot of soot on them.
Now for the kicker....when I do the old key dance with the ignition, it comes back both 51 and 52....51 being too lean and 52 being too rich, which is impossible for any vehicle to do.
I have a sneaking suspision that it could possibly be the upstream oxygen sensor, as I've already replaced the rear. I've also cleaned the throttle body and all of its sensors. I've checked and double checked all conections and vacum lines with no luck.

any help would be great, as I dont have alot of money to just start replacing sensors. Thank you very much....Koon'sXJ