Trouble shooting P0171 P0174 Bank 1 and 2 too lean

[Red Rider]

So I am gettin the dreaded P0171 P0174 Bank 1 and 2 too lean codes. Truck is a 2004 Z71 Tahoe 5.3Z engine. Truck is running smooth. No misfires or anything. So far, I have:

1. Replaced the air filter. I was not able to reset the air filter indicator but I hear those typically are not reliable (do you need to just push the button??).
2. Cleaned the Mass Air Flow MAF sensor.
3. Cleaned the throttle body without removing it. I have an electronic throttle so pushed it open to clean it. I have seen some people who push the butterfly valve open and others that say you can't because it will mess up the calibration on the electronic throttle. When I was having these codes in the past I just pushed it open manually to clean and it was good for 3 years or so.

Codes keep coming back.

Using a borrowed computer, I pulled this info:

Fuel sys 1: CL
Fuel sys 2: CL
Calc Load 2.0%
ECT 147F
STFT b1 10.2%
LTFT B1 25%
STFT B2 10.9%
LTFT B2 25%
Eng RPM 596
Veh Speed 0mph
MAF 0.73 lb/min
TPS 6.3%

So it would seem that this is happening at idle.

Any ideas of what I can try next? I am thinking of pulling the throttle body off to clean the back side as well.

Lastly, I can hear a hiss sound on the driver side of the engine. I thought it may be a vacuum leak, but when I waved a little propane there, it did not change engine idle.

Thanks

 

[Scottydoggs]

those codes are like 99% of the time a vac leak

 

[Red Rider]

The circled area is where I heard what sounded like a vacuum leak. Again the propane did not have a noticeable change in RPm. Is this normal? I saw someone use water to locate vacuum leaked. I may try this next.

 

[Scottydoggs]

see that black tube leads tot he firewall then just out side the circle is a white connector? make sure that lines not broken.

 

[Fless]

Z engine, so Flex Fuel.

Another thing to check: since the positive fuel trims present on both banks, make sure there's no unmetered air getting in after the MAF and before the throttle body. The intake pipe should be connected tightly on both ends, and check for any cracks, or small hoses being disconnected from the intake tube. IIRC there should be at least one smaller hose that connects underneath the tube.

As @Scottydoggs noted, do a careful inspection of the condition of any rubber vacuum lines on the engine. A standard vacuum test with a vacuum gauge might help find something.

If you have vacuum assisted brakes, there may be a check valve in the line to the vacuum booster. Check that to see if it's acting right (can be done during the vacuum test).

 

[tiktok4321]

I know this is an old thread, but if it helps anyone, cool. My pcv valve came off. That was all. Codes reset.