Toyota Repair: 1990 Camry 3sfe EGR valve, shade tree mechanic, combustion temperatures

Question
Ted,

Just found your column and I am looking forward to getting your input on several items.  However, my baby just failed her NOX emissions test in TX so this will have to be the first question.  The levels have been rising noticeably in the last year or so. The High/Low numbers in 2002 were 532/864; 2003 415/399; 2004 1136/1223 and now in 2005 they are 1759/1806. Passing levels are 1258/1378.

The EGR valve seems to be the popular culprit so I plan to remove it and clean it out.  Do you have any cautions or recommendations in doing this?  Is there anything else that I should address?

Is there any shade tree mechanic method to determine if the catalytic converter is working as it should?

Thanks,
Kep

Answer
The cat converter is the least likely cause, High Nox readings can be caused by a malfunctioning EGR system but this will turn the check engine light on, Is that the case?
If not, the egr system may not be the problem so let me know if the light is on, it's very important, another cause of high readings is that the combustion temperatures are too high, the EGR system was designed to reduce combustion chamber temperatures to reduce nox emission, that's it's only purpose.
If the engine is running too hot it will have a direct effect on emissions so make sure there is no overheating problem. Please get back to me with this additional information, and if there is a check engine light on I will need the trouble codes from the computer.