I was just trying to figure this out for myself... i could have sworn that I had one at one point in time, but I don't now. The other odd coincidence is that my gas gauge isn't working right. I'll fill my tank up completely, and the top notch on the gauge doesn't stay lit. I wonder if that valve might be hanging out in my tank and causing problems.
I didn't think there was a valve, but it sounds like one of your sensors may be shot. I don't know if the Celica has many sensors, or just one that floats with the gas and measures it that way, but either way it sounds like a sensor problem.