2003 buick park avenue

A couple of weeks ago,a friends 2003 Buick Park Avenue started losing acceleration power, especially noticeable on slight inclines. Gotten worse. Replaced the MAF (OEM), after trying to clean it. If the MAF sensor is unplugged, the car run fine, so the car appears to run in some default mode. Plugging the MAF back in, the car is back to hesitation/ loss of power.

No trouble codes (except when the MAF is unpugged, so the car can be driven).

Replaced the PCV. It was sticking. Also oil passed through the to the MAP sensor, so replaced the MAP sensor.

Sprayed the throttle body to eliminate carbon build up.

Replaced with a new throttle position sensor.

Temporarily swapped a working ignition control module and coils, from another Buick, to rule out the ICM and coils.

Fuel pressure at the fuel rail was good, 50 psi if I recall correctly.

Tested fuel injector pressure regulator no leaks (no fuel smell in vacuum line).

Tested for vacuum leaks twice, once spraying carb cleaner around, then a second time using propane.

Replaced the external fuel filter.

The fuel pump (with it’s fuel screen) was replaced about 2 years ago, so I can rule that out.

New air filter (wasn’t that bad, but replaced anyways).

STFT -4 to 2 (or so)

LTFT -12 to +4 (or so)

Knock = 0

No misfires on the scanner.

Tested the IAT sensor resistance with ambient outdoor temperatures. Can’t find specs online, but it does adjust to temperature. Suspect it is good.

65 degrees (morning) 2810 ohms

90 degrees (late afternoon) 1990 ohms.

The car appears to run (with MAT connected) a slightly better in the morning when cooler, then when it gets warm.

The car starts just fine. Slightly rough, but not bad.

Four months ago.

Engine was running a little rough. Also

Got a code for EGR (stuck open). Replaced.

Seemed to help. I believe this to be unrelated to the current problem, but mention it in-case.

Since the car runs good (worse gas mileage) with the MAF unplugged, I am inclined to think it is a sensor, but I have run out of sensors to replace/test.

Any suggestions on how to proceed.  I have a descent scanner, so I can give feedback for requested code.

Thanks.