Thanks for the info. The I-TEC does it mechanically, but it sounds like the principle's the same: "small amounts of exhaust gas" is the definitive term. I'm guessing that with a mechanical device, like I have, the deep vacuum of heavy acceleration is offset by the increased back pressure from the exhaust so it equalizes and keeps the EGR closed.

Anyway the stumbling problem turned out to be an incredibly fouled throttle body and a maladjustment of the throttle position sensor. From an external exam it looked OK, but when I unbolted the throttle body from the common chamber there was such a heavy build-up of greasy black soot on the back of it that the throttle plates weren't closing all the way. I guess that threw off all the other settings. One afternoon and a can of carb cleaner later I'm cruising again.