The trouble code I got was PID02 1457. On troublecodes.net the note I found was:
P1457 Unable To Pull Vacuum In Tank
This seems reasonable as I disco'd the vac hose from the charcoal cartridge and capped it for now. I can reconnect to the passive side later.
I cleared the code using my brand new Scan Gauge II, and the check-engine light went off.
After my first full tank of gas, I got 22.3 mpg - not a breakthrough, but Ron says in the Vacuum Sytems PDF
that Honda's often need a couple of tanks to show results. I think I will try that. And my exhaust temps are high, maybe higher than pre-mod (476 up to 560 or so).
This suggests to me that I need to research my vacuum leaks, maybe the TB gasket, or the Idle Air passages (two big ports, see above).
That said, I swear this car has more power and runs smoother. It seems I barely need to squeak the gas pedal to get all over town really easy, and it pulls great on the hills when I need it. We have a lot of these out here.