For what it's worth, I (meaning my indie shop) replaced the big rubber boot and I got good results - for a bit. Then my mileage crept up again, the light came on, and I got the P0171/P0174.

Took it back, and they are now telling me that it's a leak through the "manifold tuning valve", which sounds to me like the Idle Control Valve. I let them keep it overnight to get it nice and cold and they used their smoker on it and found this item leaking, so they're replacing it and I'll report back on the results. I was about to get a MAF and replace it myself but I saw Greg's results...might still have to, but we'll see.

Thanks to all!