clogged cat homie!

clogged cat can be caused by faulty bank 1 o2 sensor giving false reading causing the computer to think its running lean and dumping extra fuel. or it could be caused by either a faulty thermostat or coolant temperature sensor, which would cause the computer to do the same thing. or if its a car that utilizes a secondary air pump for emissions, a faulty solenoid would cause the vehicle to run rich, causing cat to become clogged. clogged cat can easily be checked by using a infrared temp gun to measure the temps at the front and rear of cat. if the temps are close to the same its not clogged, but if the engine side is significantly higher....bingo!

but rotten egg smell generally points to a clogged cat.
you will also notice a decrease in power, especially under load or going up steep hills. vehicle will seem to "bog" down

Problem-rotten egg smell
rotten egg smell generally points to clogged cat
Clogged cat generally caused by a rich fuel mixture condition
running rich generally caused a failure in any of sensors related to the fuel/emissions

bank 1 & 2 o2 sensors
map or maf sensor
IAT or coolant temp sensor
secondary air system
egr system

a sticking open secondary air solenoid or egr valve can cause a engine to run rich without throwing a DTC by allowing unmetered air into the exhaust system, causing bank 1 to detect a lean fuel mixture and adding fuel to compensate resulting in a unnecessary rich fuel mixture condition.