First of all the reason you don't have accurate O2 readings is because you soldered the connections instead of crimping them. When you solder the connections it doesn't allow the wire to breathe. This is very important.
Your ecu is probably compenstating for the erroneous readings from the O2 sensor. The O2 sensor isn't in the "loop" for the first couple of minutes until it heats up. That's why there are 3 wires going to it. One for the actual sensor and two for the heater.

Second I have read from other Bricksters that the Walkers are junk.
Mcduck suggestion is the favorite among the people on this board. It's the cheapest solution with the longest lasting results.