If you will poke around on the Internet, you'll find this is a common complaint about Toyotas. I know there have been Toyota Technical Service Bulletins issued for this concern. Ray O can probably shed more light on it than me.
The smell is a result of the catalytic converter creating hydrogen sulfide. Small amounts of sulfur are often in gasoline. The emission control systems for some cars tend to convert this into hydrogen sulfide, which stinks. Others convert it into sulfuric acid, which doesn't smell, but eats up exhaust systems. It is not just Toyota that has this problem, but they seem to have it more often than most other manufacturers. Maybe Ray O knows why this is the case (probably catalyst type, and temperature of the exhaust). And if you get fuel with too much sulfur, almost any car will emit hydrogen sulfide. If you regularly get the bad smell, I'd suggest switching brands of gas (although in Fayetteville, it is likely all the gas comes from only one or two sources and the only difference in the gas is the secret sauce added at the distributor). The sulfur content of all gas should be reduced over time, but mistakes are made (Shell got hammered for selling high sulfur gasoline in the Louisiana recently).
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Sulfur dioxide (SO2) is sometimes created during the combustion process from the small amount of sulfur present in gasoline. During certain conditions the catalyst oxidizes sulfur dioxide to make SO3, which reacts with water to make H2SO4 or sulfuric acid. Finally when sulfur and hydrogen react, it forms hydrogen sulfide gas. This process creates the rotten egg odor you sometimes smell when following vehicles on the highway.....
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Excerpt from TSB EG003-03, Titled SULFUR ODOR FROM EXHAUST:
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Some owners of Toyota vehicles may experience a sulfur-like or "rotten egg" odor from the exhaust system. Sulfur is a natural component of crude oil from which gasoline is refined and the amount of sulfur can be decreased through the refining process. The amount of sulfur in fuel sold in California is regulated, however gasoline sold in other states can have substantially higher sulfur content. Sulfur content also varies considerably between gasoline brands and locations.
A sulfur odor emitted from the vehicle's tailpipe does not necessarily indicate that there is an issue with the engine's running condition, but is most likely directly related to the fuel. If the vehicle is exhibiting an excessive sulfur odor, the following checks should be performed:
If the MIL light is ON, check for DTCs and repair as necessary.
If no trouble is found after performing the above check, recommend the customer try a different source of fuel. Replacement of oxygen sensors, air/fuel ratio sensors or catalytic converters will not reduce the odor and will therefore not be considered warrantable.
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Cat odor. Toyota is taking a different approach to complaints from customers regarding the rotten-egg smell that can sometimes spew from a vehicle's exhaust. While some manufacturers recommend replacing the catalytic converter as a solution to the problem, the Japanese maker is steadfast in its belief that a foul-smelling cat isn't necessarily abnormal, nor damaging to the vehicle or the persons in it. Toyota bases its theory on the fact that cat odors are typically due, in direct proportion, to the amount of sulfur present in the fuel. The higher the sulfur content, the greater the likelihood of a foul smell coming out the exhaust. And vice versa. As long as the MIL isn't illuminated and no DTCs are stored, Toyota suggests explaining to the customer that the sulfur smell is normal and no cause for alarm. Recommending that he switch to different fuel brands can often help, too, points out Toyota.
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