Rick, you need to have a computer hooked up to the car while you are driving it to check for any sensors playing up with you.
The O2 failure you originally saw was probably because of some other sensor giving a bad reading, most likely the coolant temperature sensor. If it fails, the ECU will think the engine is colder or warmer than it actually is. The ECU will then make the mixture richer or leaner, but to an extent where the O2 sensor can't really cope with it any more. The O2 sensor is only for fine tuning the mixture, and mostly while the engine is idling. The ECU will then decide that the O2 sensor is faulty, where it is actually the temperature sensor that is causing the trouble.
Inexperienced mechanics tend to do what the computer tells them to do
Are you sure the coolant temperature sensor you fitted is the correct one? There are two sensors fitted next to each other, one is for the ECU (with a green connector), the other is for the dash.
Was the cam belt job done professionally using the right tools?
- Anders