Toyota Repair: Emission test failure- toyota camry 1993, toyota camry 1993, combustion temperatures

Question
Recently, my Toyota camry 1993, 4 cyliner failed the emission test. The results are as follows:
HC ppm 62(limit is 60)- PASS
CO%  0.47(limit is 0.35) -FAIL
NO ppm 1142(limit is 457)-FAIL
My mileage is 297458 km
Had the oil change done prior to the test.
Car is running fine
Thanks for your help


Answer
High NOx emissions are usually due to an EGR system malfunction or higher than normal combustion temperatures, this could be caused by a partially restricted egr passage or a malfunctioning egr modulator valve or in rare cases the egr valve itself, the system should be tested using a vacuum gauge by someone that is familiar with EGR system operation, another but less common cause is higher than normal combustion chamber temperatures due to either an engine running hotter than normal or excessive compression due to carbon built up in the combustion chamber.