Your Toyota's oxygen sensor might be getting a bit "lazy". It seems there's a slight increase in CO emissions as well, indicating a rich mixture. Typically it's the oxygen sensor which is responsible for changes in air/fuel ratio.
We'd recommend conducting a propane enrichment test to verify the oxygen sensor's response time and voltage output, and move on from there.
If your Toyota is a V6, both oxygen sensors will need to be diagnosed (Bank 1 and Bank 2).
posted by SmogTips Support