I can't say if that company is still in business as the website looks the same as it did in 1998. I have used that cable with the software available on the RRE site, but I prefer the OBD-2 software. There are probably lots of new things out there that I don't know about. My car is from the '90s and so is most of my knowledge. You really only need three things to calculate steady state required fuel: air pressure, air temperature, and engine RPM. That means MAP, IAT, and CPK sensors. I think you can rule out CPK since that should result in much more noticeable symptoms than just some AFR drift. MAP and IAT should be your first stop. If one of those is reading incorrectly, the ECU will calculate required fuel incorrectly, and have to compensate with LTFT and STFT based on output from the front narrowband O2. I think you will find that the CLT sensor is most critical at start-up on a cold engine and when the IAT is not available (disconnected or considered failed by ECU). At some point with a normal engine warming up, the ECU will stop using the CLT to calculate fuel and start using the IAT. Not being privy to the code, I can't say exactly when and how that occurs. Short story, I would look closely at MAP and IAT output.
