catalytic converter. if u have never changed the 02 sensor a bad one will destroy the converter. if u have changed the converter then try the pcv valve and air filter. the high heat and humidity with the gasoline blends on the market can mess things up too. the higher alcohol content in the gas makes the earlier hondas not run well. oil cos add alcohol to make engines run leaner and they also use it as a cheap way to increase the octane.. so u burn it faster and it doesnt help the engine any. makes it run like crap. it could also be that u r using a bosch sensor. older hondas do better with ngk/ntk or denso sensors. ngk makes the oem for honda.