One other thing I forgot to mention is the brake feel - they're firm and solid, so that's an indicator of increased manifold vacuum. Groove is working!
My OBD-II app indicates at hot idle/closed loop the throttle angle is 1.57%, another indicator of success.
Back to mileage and re-learn: I've already mentioned a tune-up is upcoming, with increased plug gaps, but I'm also going to spring for those sexy Granatelli Zero Ohm wires and a hotter coil to go with the fine wire iridium plugs I have. Another thing that will improve mileage is replacing the wheel bearings - I mentioned this before that the front ones need replacing; surely they're presenting a drain on powertrain efficiency. And while I'm in the wheels, I'm going to do front brakes as well, because one of the discs is warped.
so yeah, as it stands now, rough, ballpark, horseshoes and handgrenades guesstimate numbers for improvements in mileage as I can recall them: when I first got this vehicle, it was all I could do to get a readout on the dash from the computer that said 10L/100km cruising around town and 12-13 on the highway with a lighter foot. The PCV re-route and switching to 89-octane E5 gasoline took those numbers down to 5.5-6L/100km in town and 8.5-9L/100km in the highway. Now, with the groove added, the city numbers haven't changed (yet, I hope), but at the speed limit on the highway (without the Cruise control engaged), the dash readout says about 7.0L/100km. If you remember from earlier in this thread I posted the published Gov't ratings from the window sticker when Gradndad bought the thing 10 years ago, I should be seeing consumption of 12.6L/100km in the city and 8.5 on the highway...needless to say, this package of mods, a change in fuelling and a less aggressive driving style has brought about gains somewhere in the range of ~50% on average, and I'm looking to push that somewhat farther with some vehicle repairs/overdue maintenance.
The Groove WORKS, friends, if you follow the directions.
Stay tuned for further improvements in the near future. I'm looking to take this vehicle on a 400-ish mile highway trip in a few weeks after this is all done. That will give a super indication of what's really going on.