Please explain this code: P0466 Purge Flow Sensor Circuit Range/Performance

[GasSavers_StanleyD]

The followingScanguage code came up in '97 Toyota 4 Runner:

P0466 Purge Flow Sensor Circuit Range/Performance .

Anyome know what this is? Is is related to O2 sensor or Mass Air Flow sensor. I have know idea what this is and would like to know what it does and an idea of how much it costs to replace. Can I do it myself or is this shop-only job. Im a little mechanical but dont really know much. I also dont want to get railroaded by mechanic by going there without any knowledge or info.
I need to get the car inspected but the engine light came on and according to Scanguage and OBD2, its not ready because ofthis crap. Ive cleared the code, bu the Scanguage still reports that the car is not ready for emissions testing. I wil have to figure outwhat test is not complete. Im hoping that there a car-techy here that can help.