Firewall is the "wall" that seperates the engine from the cabin from the bottom of the windshield to where the floor begins. I have to change mine out this weekend and the tips I got were to let the enging run at about 2500 rpm for 15 mins to heat the manifold. I plan on changing it this Friday and will Kroil (better than WD-40) the hell out of it tonight. Bank 1 Sensor 1 is the firewall sensor as per the Toyota techs. We'll see.
