maxima_million

My check engine light came on. I checked the codes (39 [undefined] and 75 [EVAP Control System]) and reset the ECU. The light went out AND my gas mileage increased ALOT!!!! About 5 days later, the same codes popped up. I read some of the posts about this, but could not find an answer to:

1. How difficult is it to replace the EVAP Control System?
2. Does anyone have info on how to replace it? Possible digital pictures?
3. I don't have a repair manual for my '98 Max... any suggestions as to which one is better???

Thanks in advance!