Toyota Repair: Nox emissions, nox emissions, emissions test

Question
My 1991 Camry just failed an emissions test because of high Nox.  I understand one thing that could help is to clean the EGR valve.  Where is it located?  Also, can you recommend any other simple steps that might help pass the test without spending a lot?

Answer
If there was an EGR malfunction the check engine light would be on, is this the case?
High NOX readings are a direct result of higher than normal combustion chamber temperatures, this can be caused by carbon builtup, incorrect engine timing,engine running hotter than normal or as I said, an EGR system that is inefficient, you can have the compression checked and if it is a lot higher than normal carbon on top of the pistons and in the combustion chamber may be the problem, this engine also uses a three-way catalist system and the converter is supposed to reduce some of the NOX so there is another possibility but it is not as common as the aforementioned ones. In your reply can you let me know what all the readings were(HC,CO,O2and NOX)is it a V-6 0r 4cylinder, this information can help me make a possible diagnosis.