I've got a 97 4WD Rav that I've been trying to get better mileage with for quiute a while now. I got a scan tool that runs on my plam pilot and I've found one thing that seems to be a problem, but can't determine what's causing it. Anytime I'm driving over 65mph it switches to open loop and my o2 sensor reads about 0.85v steady. I know it's supposed to switch to open loop during hard accel and when the engine is under a heavy load, but crusing on level ground @ 65mph doesn't seem like it should cause this. I got better mileage (23mpg) on a trip with mostly winding up and down through mountain passes than I did driving straight up the interstate (20mpg) @ 70mph. Any ideas what would cause it to switch over to open loop so easily? Oh yeah, I tried changing out the o2 sensor, but that had no effect at all.