93 4x4 - new O2 sensor, check engine still on

I have a 93 4x4 with a 22re and manual tranny. the previous owner rebuilt the engine recently (<5000k). the check engine light was burned out when I bought it. I fixed that, discovered a code 21 (oxygen sensor) and 25 (lean condition). I discovered the wires to the sensor were a little mangled, so I cut a harness from a junkyard and spliced it in, soldered the joints to make sure they were good. replaced the oxygen sensor with a bosch unit. the code 25 went away but the code 21 is still there! what should I do next?

the truck also idles high, (1100-1200 rpm when warm) even though the throttle stop is set as low as it can go and the air screw is screwed almost all the way in. I have checked for vacuum leaks, it has all new vacuum hoses.

thanks