Porsche Forum - Porsche Enthusiast Forums - What produces excess nitrous oxide in a car emission?

The simple answer is that you probably need to replace the oxygen sensor in your car. On older cars this is to be expected; oxygen sensors wear out over time and when they do, they no longer provide your car's computer with the information it needs to do its job correctly, resulting in high emissions. If the oxygen sensor is the problem, it should show up on a computer diagnostic test. The other possibility is that the fuel injectors are fouled, preventing the engine from getting enough fuel, and either need to be replaced or cleaned.

Nitrous oxide is the product of a reaction between nitrogen and oxygen at high temperatures. Both gasses are prevalent in our atmosphere (nitrogen alone makes up about 80% of the air we breath) and the high temperature needed to react these two gasses to form nitrous oxide occurs during the combustion process. However, a car with fuel injection like your Camry uses sensors and a computer to determine how much fuel to mix with the air the engine is 'breathing' to make sure that all of the fuel and air is burned. If you have too much fuel left over (the mixture is rich - not enough oxygen) then you get excess hydrocarbons, which is what the catalytic converter is designed to take care of. If you have too much oxygen (the mixture is lean - not enough fuel) then you end up with oxygen that wants to react with other things, such as the nitrogen in the air. Your car is running lean, hence the higher-than-acceptable nitrous oxide levels.

To replace the oxygen sensor, with parts and labor, you're probably looking at a couple hundred dollars. If the fuel injectors need to be replaced, it'll cost a lot more. The actual parts aren't very expensive, but the labor to replace these parts is time consuming. If you know anyone handy with cars, you could buy the parts and have him/her install them and save yourself a significant amount of money.

Good luck!