Ok, so I took my 1993 Toyota Camry 4 cylinder in to be smogged today fully expecting it to be a smooth process.  Well, they called me up and told me that the car has high NOx emissions so it couldn't pass smog.  That, and they want like $150 just to test for what is wrong. 
So, I did a little research and I found that it is Oxides of Nitrogen? What is that? Is it just one of the byproducts of burning fuel? What could cause high emissions of NOx?
My car is fully stock with no "performance" upgrades at all. Just the regular maint' like spark plugs, brakes, oil and stuff like that. The only thing I can think of is that when my car overheated for a bit, the thermostat seems to always be a little open so the engine runs kind of cool. That would cause the engine to burn more fuel, so would it cause the high NOx emissions?
If anyone else has any ideas, it would be greatly appreciated. Thanks!
EDIT: I replaced the spark plugs with the Bosch Platinum +2's about a year ago. THe car is at 112k miles and the timing belt was replaced at around 83k. Oil changed about a month ago and can't remember anything else.
			
			So, I did a little research and I found that it is Oxides of Nitrogen? What is that? Is it just one of the byproducts of burning fuel? What could cause high emissions of NOx?
My car is fully stock with no "performance" upgrades at all. Just the regular maint' like spark plugs, brakes, oil and stuff like that. The only thing I can think of is that when my car overheated for a bit, the thermostat seems to always be a little open so the engine runs kind of cool. That would cause the engine to burn more fuel, so would it cause the high NOx emissions?
If anyone else has any ideas, it would be greatly appreciated. Thanks!
EDIT: I replaced the spark plugs with the Bosch Platinum +2's about a year ago. THe car is at 112k miles and the timing belt was replaced at around 83k. Oil changed about a month ago and can't remember anything else.
				
		
			