nasty P0171 code

[techteacher]

The car is an 2007 base Vibe 2WD. I'd posted about an intake earlier in the month of March. Doesn't sound likely that swapping one would work. I will revisit the intake gasket since my shop didn't use the OEM Toyota gasket.
All the work done to the car has been by me (limited), or one of my two friends who have considerable knowledge and abilities and who each own repair shops.
nothing, and I mean NOTHING has worked to clear the cel code P0171.
here's what has been done:
MAF sensor (twice- just to rule of a defective part)
pcv value and hoses
intake gasket (not oem)
system was hooked up to smog machine with no leaks detected so we tried the Front O2 sensor
most recently in the month of March
fuel pump ( scanner showed some goofy readings when cranking so we thought perhaps the Fuel pump was erratic)
rear O2 sensor
computer under the glove box was one serial number off the list on numbers in a TSB for bad computers so we bought and flashed a new computer
I'd tried Techtron fuel injector cleaner but didn't know how long it would take to dissolve what was there so 4 new fuel injectors went in yesterday.
NOTHING has made an impact on the return of the P0171 code.

The state inspection sticker ran out yesterday, so I'm totally frustrated by this code and can't believe that nothing has worked as yet.

Car seems to run fine no matter what, the only thing that appears off is that sometimes there's extended cranking when starting the car. (another thing that made us think it may have been a fuel pump/fuel pressure issue)

The exhaust system has been looked over but nothing really stands out as a possible leak, but since i live near Syracuse NY (aka Salt City USA- a moniker earned by the history of being a salt producer in the 1800's, but one that very effectively describes the road maintenance program & how we make it through the lake effect snows each winter) corrosion of any metal parts can't be ruled out 100% visually.

Open to suggestions, cause I'm basically up Schitt's Creek , and I think my paddle just floated away,,,,,,,,,,

[vibrologist]

Rather than the smog machine you may use a MAF sensor cleaner to spray at potential vacuum leaks. Don't for get the unusual ones: oil filler cap, brake booster hose. Also consider removing the injectors and testing them/cleaning them (youtube for diy cleaning).

good luck!

[petervivian]

Looks like they have changed/cleaned the MAF sensor twice already.
Did you check any other possible leak other than the exhaust?

[vibrologist]

To clarify: you may idle the engine and spray carb cleaner/ maf sensor cleaner around suspect areas in order to detect a vacuum leak. The engine sound will change when the flammables get sucked in. Voila, there is your vacuum leak.

[jolt]

There is one post here on this board where the the person had a cracked intake manifold which caused the P0171 code.
viewtopic.php?f=17&t=43883&p=501522&hilit=P0171#p501522
Here you can read about it. The odds are not real high on this being the problem, but as this shows, it does happen.

Did you check your brake power booster for vacuum leaks? Check your throttle shaft for vacuum leaks? Check all connections between MAF sensor and cylinder head for vacuum leaks. What is your fuel pressure? You never said you checked the fuel pressure. When you replaced the fuel pump, which does not control the fuel pressure, was it just the pump or the whole pump assembly with fuel level sender? Is the Vibe stock, no after market air filter, intake manifold, etc. ? Did you pull the battery cable to clear the ECM and let it build a new profile or just clear the codes?

Here is a post I ran across on another board:
"I had this too. Just prior to my final repair, my long term trim was running 39%. The car ran pretty good and even passed an echeck by using the gas analyzed for emissions. but the light had been on over a year. I started the saga by cleaned the Mass air flow sensor. No luck. A mechanic replaced the MAF sensor and it went away for a while. When it came back, the mechanic replaced the intake gasket. He also measured the fuel pressure at 42 psi. Low but not terrible. No help. After several months I replaced the O2 sensor and cleaned the MAF sensor, no help. I looked hard for vacuum leaks, but found nothing. While at a toyota service department at a dealer, I chatted with a service guy on this. He interrogated me on all the stuff above. MAF sensor, O@ sensor. I asked if a fuel filter or fuel pump was in order. He looked knowingly at me and said don't go there. He said, replace the fuel injectors. I got a set of 4 with a fuel manifold from a local yard from a 2002 prism for 75 bucks. Slapped them in. right away the short term trim was running -23%. Good sign. I left it with the light on. I got a call from the owner in a few hours, the light switched off. So my question is, what should I get the service guy. Case of beer, pizza, doughnuts, or a bottle?"

On that note, one can of injector cleaner is not going to do anything if the injectors are causing the code. Fuel filter? That is in the fuel tank and is part of the pump assembly and is not a real good filter. At least not to filter down to the particle size that can mess with a fuel injector. The fuel pressure regulator is also part of the fuel pump assembly but if you just replaced the pump/motor and not the assembly, then the fuel filter and pressure regulator did not get replaced.

What are your fuel trim levels at idle, under load, and at highway speed? A list of parts that were replaced does not help troubleshoot the problem. Testing and values (numbers) are needed to know what is good and what may be bad.