Gunk and gum in the throttle body butterfly not letting it close completely on the up tip side?

How much AIR does the MAF say is going into the engine?At idle, when things are right, I've been surprised to see numbers as low as 5.3 as low as 4.8 or 9...

 

Thanks for the suggestions everyone! I finally found the issue. The circular "front manifold gasket" that joins the upper manifold and the "elbow" to the throttle body (this part is unnamed in the drawings I have seen) was leaking. Evidentially, when the manifold gaskets and throttle body were replaced, this one was omitted. I rigged a smoke test by taping a tube to the inlet from the left valve cover and blowing cigarette smoke into the plugged off throttle body. Nearly passed out from smoking that much to fill the chamber, but did find some smoke coming from the general area downstream of the throttle body. Then I verified the location with a strip of tissue paper while blowing on the tube. Once this leak was finally located, I was able to remove the throttle body and this elbow without that much effort and ordered the rare gasket from parts geek. My S type is now purring like a happy house cat once again. Although I am very disappointed in the shop that did the diagnosis to begin with, and myself for trusting their abilities, I have new confidence that I can make progress on my old jag with persistence and patience.

While I was waiting on this part, I replaced the fuel injector connectors. I was nervous about doing this, but the old connectors where brittle and had been held in place with a dab of silicone. This worked as a bandage, but made diagnosis of the lean fuel codes difficult. I used heat activated wire connectors that both glue the wire insulation and solder the wires together with a heat gun at 500 degrees. The entire process took about an hour and cost around $50 with the heat gun. I don't think the engine should produce enough heat to cause issues with the connectors and know the connection is solid.

I hope someone who is struggling with their beloved Jag may find this helpful.

Thanks again everyone, talk to you soon!