2005 S60 2.5T AWD OBD Code P2177

[jemulator]

Hello all, new member.

I have been helping my father troubleshoot his 2005 S60 2.5T AWD coming up with code P2177 LTFT too high at low load. Volvo code ECM-212C

So far:
replaced MAF sensor, MAF readings match required values at idle(3 g/s), low load(9-15 g/s)
Checked Catalytic COnverter with camera and it was clean.
Replaced both O2 sensors.
replaced fuel filter, Fuel pressure is 55 psi for 5 seconds on start, then 44 PSI at idle, low load, and heavy load. Fuel pressure never comes up to 55 PSI like it should while driving, except for random times it does spike up for a second then comes back down. Seen it go as high as 86 for a split second on the Diag reader. Thinking this is a symptom rather than the cause, because it religiously goes up to 55 at startup so the FP regulation system seems to have control. Noticed the fuel system sporadically goes in and out of open/closed loop rapidly while driving, again probably a symptom of whatever is the problem. Could the ECM be keeping the fuel pressure at 44 because of the fault code?
Fixed several vacuum/boost leaks. Tried smoke test, no results. Tried acetylene to find leaks, no results.
Checked The Brake Booster and vac assist pump by isolating both from intake but no change. Brake Booster holds vacuum for hours after car is shut off.
Vehicle has brand new radiator/intercooler.
Disconnected the battery for 2 hours but code and high LTFT bank 1 comes right back. LTFT=16 to 20 at idle and while driving.

Only thing we can come up with is to try to pressurize the intake system after the MAF to find a leak, but not sure exactly if theres anything to watch out for when doing this, overpressurizing something, etc. Volvo recommends pinching the crankcase vent hose and disconnecting the lower purge valve hose, opening the oil cap, and using 4.5psi to pressurize the system, while using soap bubbles.
One other thing to try is the fuel regulator test by jumping out the FP relay and looking for 55 psi, according to VIDA.

Convinced there must be an intake or boost leak somewhere just how to find it?

PS, initially driving the car in a flood caused a wet air filter and about when the code first came up. Not sure if this was the initial cause or what might have happened as a result of that much moisture in the intake system.
The Turbo always makes a squeeling sound when driving in the rain for a while.

Any advice would be appreciated, needless to say, major frustration has set in.
Thanks!

[precopster]

Glad you added the P.S !!

If the car had been driven in to a flood you had better remove ALL connectors in the engine bay and imspect for corrosion THEN spray with contact cleaner THEN re apply dialectric grease to connectors.

Also remove engine and trans ECUs and clean edge connectors thoroughly with toothbrush and contact cleaner.