About your O2 sensor(s), hopefully your scan tool is capable of capturing and monitoring O2 sensor voltages in real time. If it has this ability, is is exactly the menu you need to use. First, insert the key into the ignition switch an turn it to detent just short of activating the starter; in this position, the entire car's FI system is energized and ready to fire. O2 sensors provide a straight base line voltage value at rest, meaning not actually reading 02 content. All primary and post car sensors should have the same baseline number on the scanner's screen, if I recall correctly. If a sensor is malfunctioning, it will not even likely provide the right baseline voltage and this is how you can tell if a O2 sensor is on its way out.
One step further, O2 sensors provide a predictable oscillating voltage signal in the form of a sine wave. If your scan tool can read real time O2 signal voltages, this is what you want to see for each primary O2 sensor. If you see an erratic wave on the scope function of your scan tool, that is a sure give away the O2 sensor is beyond its useful life, and replacement is warranted.
As for your VANOS problems, call Dr VANOS, this is the real vendors name, not some attempt at humor here, and ask him specifically what test you should perform to determine if the VANOS module on your sled is indeed experiencing intermittent failure, leading to your current predicament. There are more sophisticated scan tools that I believe can make the module activate a specific solenoid in the module; a year or so ago, I remember playing around with my buddy's expensive scan tool and manually activating a solenoid (when the car was at rest of course), and it made a faint "click" so this is a sure indicator the that the individual solenoid is working. That Scan tool was a $3,000 piece of equipment btw. Good luck fellah.