Things are continuing to look optimistic for the Toyota. I've been enjoying tinkering with it. I grabbed a can of MAF cleaner from my box at work and sprayed the MAF sensor down. It wasn't very dirty but cleaning it won't hurt. I ordered a gas cap, cost a whopping $14. I'm waiting for that to come in. I pulled the PCV valve out and cleaned it with some brake cleaner. It wasn't stuck or very dirty, but it had some crud in it. I spent a good bit of time inspecting the engine bay, and I'm wondering how much of the oil loss might actually be from leaks. Even though the valve cover gasket was changed not long ago, it's looking a little wet, and the timing cover is very wet. There is also quite a bit of oil seepage where the lower half of the block mates to the upper half. The drain plug gasket is chewed up and is causing the drain plug to have a drip.
So I'm gonna have to get it cleaned up and see where it's actually leaking from and how badly. Some simple green and a pressure washer will make quick work of that. I think after that, my next step in investigating the P0420/P0171 will be to borrow a picoscope from work and see what kind of waveforms the O2 sensors put out.