Even in Kyoto

All good advice. Not sure why the car would feel noticeably smoother after an oil change... the oil should never get that bad that you could tell the difference, and the oil looked fine before you left (still a nice honey color). Maybe an intake air filter was changed too? That's more likely to be noticeable. And looking at that diagram more, it would be the intake manifold. With the computer controlling everything, there's not really anything to tune. It constantly adjusts everything itself. And yeah, responding to both posts in one go. If not a bad connection (sometimes unplugging and re-plugging those little automotive connectors a few times gets them working for a while longer), wires will break from the vibration too, or start to get a spotty connection. Could poke at either connectors or wires with the multimeter.