Fighting a lean condition

[Jeff G 78]

First, a little background info. I bought my '78 280Z 17 years ago and due to many factors, it hasn't been on the road until late last fall. I rebuilt the engine years ago with flat top pistons and an N47 head. I have driven the car around 200 miles total over several days. I have the stock cam in the car right now, BTW, not the cam in my sig. When I rebuilt the engine, I bought new injectors and had them flow matched. The fuel tank has been cleaned and relined w/POR15 and the filter is new. Fuel pressure reads where it should per the FSM at idle, but I haven't tested it under load yet.

The car runs decent when cold, but begins to stumble when warm and by the time it has been run for 15-20 minutes, it misses under load. When I pull the plugs after a drive, they show a lean condition. The ambient temp does not matter. It does this from 40F to 80F ambient (this is what I've tried - likely at all temps). I thought that the water temp sensor could be to blame, but it checks out per the FSM. If I disconnect the temp sensor at the bullet connector while the car is running, it nearly stalls and runs very poorly. If I run it that way for even 10 seconds, the plugs turn black and sooty. I let it sit overnight and checked the plugs after only a few minute drive before the car had a chance to fully warm up and they looked much better. I have checked all of the F.I. components via the FSM, and everything appears to be within spec. My vacuum is a tad low, but not terrible at 16 inches at 850 RPM. I have used propane to check for vac leaks, but didn't find any. If I pull the dipstick, or any small vacuum line, it drops RPM as it should. The BCDD also appears to be working, but might need some adjustment. The revs hang at around 2000 until the car drops to about 10-15 MPH. Does that sound right, or am I right in thinking that it should drop to idle sooner?

Could the Aux Air Regulator be letting unmetered air in if it is frozen open? If so, is there an easy way to block the AAR without removing it completely and making a block off plate? What else should I try? I was thinking of adding a rheostat in place of the temp sensor temporarily to richen it up when warm until I figure this thing out.