O2 & MAP testing....

Hey all
Is there any way to test the O2 sensor & MAP? I'm trying to figure out what would cause a "PO171 system too lean bank 1" code. So any testing ideas ?
Thanks for any help.....
Curt (aka Xtreme XJ)

This is also my question (kinda) & a bump for Xtreme XJ.
How do you test the MAP sensor? ('91 / 4.0)
Can the sensor be tested off the JEEP?

I've tested the MAP sensor from a Renix. I use the 5VDC off of an old computer power supply to excite it and use a hand powered vacuum tester connected to the map port. Same scheme probably works for a post-Renix map as well.