P0420 2008Toyota Avalon -

Question

My 2008 avalon engine light came on.i ran car for a while.the more I ran it the rougher the
Car began to ride,

Answer 1

P0420 Catalytic system effiecincy below threshold (bank 1)

Reason for DTC : Possible lean misfire, oil seepage in sparkplug well, MAF (mass airflow) duct causing false air, VVT system ,

Related TSB: T-SB-0105-11 MIL on OCV (oil control valve), T-SB-0047-10 ignition system mulitple ignition coil DTC

When the engine at idle and it begins to have a lean misfire, check the sparkplug well for oil seepage , What deteriates a catlaytic convertor are misfires, what eventually happens is the catalytic gets plugged up, The code you have is a result of a lean misfire, Replacing the catalytic will without having the engine performance evaluated will only lead to a hobby of replacing the catalytic convertor and having a rough idle.