Toyota Repair: 2000 4Runner - Check Engine light, emmision, gas tank

Question
Two days ago Check engine light came on - had scan/check performed and they said it was two codes in the emissions line (sorry, I don't know what they are). They turned light off & said to first try RXP in the gas tank. Check engine light has come on again this AM.  4Runner seems to run fine otherwise.  117,000 miles.  Should I take in asap somewhere for them to correct whatever these "emissions" problems are?  What possible problems are we looking at?  

Answer
Amy,

Most emmision problems are not a serious issue, but if something else goes wrong your check engine light is already on and you would not know of any other problems so try to get it fixed when you can.  If it set a PO440 code something as simple as you forgetting to tighten the gas cap or fueling with the engine running can cause this.  You may want to replace the fuel cap as maintanence item anyway since they have a check valve which can go bad causing this problem.