You're getting there. How are the connections and terminals for all fuel mixture calculation sensors? I.e. MAF, temp, knock, ... If that unplugging helps, then it might just be a case of old terminals.

 

Contacts look all shiny and new.

None of the connectors appear to look questionable.

 

Finally got to the bottom of this!

After driving for too long of a time with the LTFT at 10.something, it was the TPS that was the root of the problem!

The car drove fine, it just had really bad fuel mileage. No check engine lights, no smoke, not really any other symptom, other than poor fuel economy.

I replaced the TPS, with a brand new one, a week ago and my LTFT is at 0.0! I had a spare old TPS that I inherited as part of a used bin of XJS parts and it did not help. I will take this TPS apart and see whats doing.

I do want to note that the new OEM TPS no longer carries the Ford branding that the original parts bore. Also they come with silver pozi screws, instead of brass torx screws. The plate that holds them in also is silver in color, not the old brass color. Thought I would mention that. It was purchased directly from JDHT.