After UIM cleanup I got 1131--Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1.
So... knowing not to trust most recent work I went ahead and promptly pulled UIM again. Well, in reality I needed to clean LIM too, so that was required anyway.
In the process I rechecked all the gaskets and everything seems OK. All gaskets are new, and this is like 5th overhaul for me, so I doubt it's my sloppiness. Idle is normal, the car feels normal, returns to idle fast.
Here's the weired part. When I watch the sensor in real time Bank 1 Sensor 1 reads anywhere from 0.05 to 0.9 at first. Later, as the car heats up (I guess) it stays near 0.1
Bank 2 sensor 1 reads from 0.1 to 0.8 all the time.
So I'm thinking it IS the HEGO sensor. I might have a slightly used from my '96 somewhere in the basement. failing that, I'll swap front and rear just to be sure it is indeed HEGO, and not a leak.
Opinions welcome.
