P0171 that came back

I had a P0171 code that I thought was the MAF sensor. After cleaning it with MAF cleaner, it still had the code. Checking the intake air temperature, I observed that the temperature appeared to skew higher, even when the engine was never run, the longer the MAF was powered on. Obviously bad IAT sensor on the MAF could cause the lean condition since the ECU would not know the correct air density, so I replaced it. The P0171 still returns intermittently however.

I've checked the MAP sensor values while running at idle and high RPMs and it always settles around 30-33 kPa, which my understanding suggests there's no leak. The fuel trim, however, is averaging close to 35% which seems really high. Should I smoke test for a vacuum leak, or figure out the rig to do the PITA fuel pressure test? Thank you.

 

Since the fuel pressure test kit was free as a loaner at the car parts store, I did a quick pressure test and smoke test. The smoke test bore out a problem, it's a fuel injector seal, probably a bad one replacement when I did my head gasket. Also, why I don't see the vacuum leak in any of the hoses nor in the MAP sensor. Ordered OEM seals and goign to replace then redo the smoke test. Thanks everyone!

 

Status: Vacuum leak fixed, I replaced the injector seals with OEM ones. The aftermarket seals, just over a year old, were kinda hard and I can see why they didn't work too well. Fuel trim is still high, 25-30% LTFT, and I'm suspecting the AF and O2 sensors, even though they pass the AF test in the service manual. When driving, however, I noticed the AF sensor reporting 3.25-3.35V (where it should be?) while the O2 sensor is reporting .8 volts, which is rich. I suspect the aged AF sensor is still able to detect obviously rich and obviously lean conditions, while being a bit ouf of range for less rich conditions?