Hi

Your 97 vehicle should have 4 oxygen sensors fitted to it, try monitoring all 4 sensors and post the results of your findings. Values starting from a "Cold Start" through the "Warm Up" cycle would be a good combination to form an overview. Also if you can access the Adaptation Values for Idle and Partial Load (AKA-Fuel Trim) post them as well. Would also like to see your HFM Voltage and the Air Mass to get a better sense of what may be happening.

Thanks