Any exhaust leaks especially on the left side (Bank 2). Pay special attention to the EGR tube. DOUBLE check the vacuum lines to/from the DPFE sensor. The exhaust gas is hard on rubber parts. These lines are very hard to inspect due to interference from the Firewall.
Any intake vacuum leaks? Consider getting a propane based leak detector. I have never been a fan of spraying carb/coke cleaner all over a motor. The solvents can damage gaskets thus trading one problem for another.
Amazon.com: Vacuum Leak Detector: Automotive
Pay attention to any vacuum leak sources that can affect only bank 2. Such as the left side intake manifold or left side valve cover gaskets.
Have you tested the fuel pressure?
Any tests at all?
>>>from Ford service CD (96).
H41 DTCs P0172, P0174, P0171 AND P0175: FUEL SYSTEM AT THE CORRECTED ADAPTIVE LIMITS
Diagnostic Trouble Codes (DTCs) P0171 bank (1) (cylinder #1) and DTC P0174 bank (2) indicate the fuel/air ratio is too lean. The fuel adaptive system is at the rich correction limit.
DTC P0172 bank (1) and DTC P0175 bank (2) indicate the fuel/air ratio is too rich. The fuel adaptive system is at the lean correction limit.
DTCs HO2S Reference list:
-- HO2S-11 = DTCs P0171 and P0172
-- HO2S-21 = DTCs P0174 and P0175
Possible causes:
Fuel system
-- Excessive fuel pressure.
-- Leaking fuel injector(s).
-- Leaking fuel pressure regulator.
-- Low fuel pressure.
-- Contaminated injector(s)
Induction system-- Air leaks after the MAF.
-- Vacuum leaks.
-- Restricted air inlet.
-- PCV system.
-- Fuel purge system.
-- Improperly seated dip stick.
EGR-- Leaking gasket.
-- Stuck open EGR valve.
-- Leaking diaphragm.
Base engine-- Oil overfill.
-- Cam timing.
-- Cylinder compression.
-- Exhaust leaks before or near the HO2S's.
l Check air intake for leaks, obstructions and damage.
l Check air filter, air filter housing for blockage.
l Verify integrity of the PCV system.
l Check for vacuum leaks.