Lexus Repair: Rotten eggs odor, lexus ls 430, catalytic convertor

Question
Zak,

What do you mean by "running rich"?
I do not pick up the smell from other cars running in front of me.
Any other suggestions?
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Followup To
Question -
Hello Zak,

I have a Lexus LS-430 since 2001 when I purchased it new. Since the begining I had a very strong odor (like rotten eggs) every time I accelerate (pass or merge) and increase the speed to above 40mph. Obviously I do not floor it, I drive normal. I took it to the dealer couple of times, and they keep telling me it's the gas I use.  Lexus told me the same. I always use only reputable gas (Exxon, Mobil). This phenomenon does not happen all the time, and it does not matter how the weather is or if engine is cold or warm. The car just got out of the warranty and I still feel the smell. Sometime is really awfull. Any ideas?
Answer -
It sounds like it is running rich at times, hard to say why. This could be covered under the 5yr 60k warranty, you may be above the miles by now. You may also be picking up the smell from cars in front of you if you keep your air set on fresh air.  

Answer
There is only two things that will make your car smell like that, bad catalytic convertor, or to much fuel being run through the motor. Neither should you smell while driving unless you have a exhaust leak at the front of the motor. All the exhaust smell should be going out the back of the car. May also be (small chance) battery over charging.