1998 Volvo V70 P0172.

Apologize now, what I think I need is to write this out and possibly answer my own question before I start looking for the problem. The question is: My OBDII diagnostic will attempt to clear the code, the Check Eng Lite extinguishes but the code remains set, "Pending P0172". If a vacuum leak were constant, would cause code to be continually set. If MAF were faulty, would cause code to be continually set. Am I going down the right track so far? If a bad O2 sensor, not seeing a fault code or is P0172 higher code and masking the O2 sensor code?
Great site!
Thanks in advance.
David Willburn
Philly