According to your question, your Toyota Camry appears to be running rich. This is indicated in the high CO at 25mph. We recommend a smog station conducting a "fuel feed back" test.
This includes ensuring your Camry's oxygen sensor(s) is working properly, the ECM (engine control module) is receiving O2 sensor signal(s), the ECM is computing the data properly and sending the correct signals to the fuel injectors to either increase or decrease fuel delivery.
The feed back test will utilize a 5-gas analyzer (usually a smog machine) and propane. Propane is introduced to the intake system while monitoring the oxygen sensor reading. This test should be done after the engine has sufficiently warmed up and while it is running at idle. The added propane should increase O2 sensor voltage output and the ECM should lower injector pulse rates. If there is no increase in oxygen sensor voltage, your Honda might have a defective O2 sensor. The sensor should be replaced and the test repeated. If voltage increase is present at the sensor output the technician needs to ensure voltage increase is also present at the ECM O2 input terminal. If voltage is present at the terminal as well next the technician must ensure the computer output terminal to the fuel injectors are lowering “injector pulse rates”.
At the end of the feedback test it will be know whether the high CO fault is electronic or mechanical, and the technician can further diagnose the fault.
Your Toyota Camry also has other emission sensors which send vital engine information to the ECM as well, such as the TPS (Throttle Position Sensor), ECT (Engine Coolant Temperature Sensor) and the MAP or MAS (Vacuum/Pressure Sensor). These components should be inspected as well. They are also part of the "feedback test" and control fuel delivery.
For more information... What Causes High CO?
