Took to inspection code p0171 - 1996 Oldsmobile LSS

Clean the MAF sensor. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling Inspect all vacuum and PCV hoses, replace/repair as required Inspect all hoses and connections in the air intake system Inspect and/or test the intake manifold gaskets for leakage Check for a dirty fuel filter and proper fuel pressure Ideally you'll want to monitor short and long term fuel trims using an advanced scan tool If you have access, you may want to run a smoke test

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System Too Lean P0171
Clean the MAF sensor and IAC valve with MAF cleaner
Inspect all vacuum and PCV hoses, replace/repair as required.
Inspect all hoses and connections in the air intake system.
Inspect and/or test the intake manifold gaskets for leakage.
Check for a dirty fuel filter and proper fuel pressure.

As a last resort, replace O2 sensor

System Too Lean P0174
Error code P0174 is described as System Too Lean (Bank 2). This means there is incorrect ratio of air and fuel on the car's engine system, specifically on Bank 2 of the Cylinder. “Too Lean” means there is too much oxygen in the exhaust.

As a last resort, replace O2 sensor

try replacing the o2 (oxygen) sensors on the exhaust pipes. there should be at least 2 of them.
if that does not work then your next option would be to have the catalytic converter inspected to see if it is plugged. (poor acceleration)

You did a lot of work, could be dirty fuel system try sea foam I did on my friend car go away.

Hyundai has P0171 and P0170 codes. What does this mean??...and took it to Autozone to run a check engine light test on it. The codes that came back were P0171 and P0170? The possible problems were system too lean, fuel syst fault, ignition syt fault, en...

p0171 and p0174 both banks lean

What does that mean? Basically this means that an oxygen sensor in bank 1 detected a lean condition (too much oxygen in the exhaust). On V6/V8/V10 engines, Bank 1 is the side of the engine that has cylinder #1.
Note: This DTC is very similar to P0174, and in fact your vehicle may show both codes at the same time.
Symptoms You will more than likely not notice any drivability problems, although there may be symptoms such as a lack of power, detonation (spark knock), and/or a hesitation/surge on acceleration.
Causes A code P0171 may mean that one or more of the following has happened:

• The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
• There could be a vacuum leak downstream of the MAF sensor.

P0171 - System too Lean (Bank 1)
P0174 - System too Lean (Bank 2)
P1451 - EVAP Control System Canister Vent Solenoid Circuit Malfunction
I'm afraid I don't have enough info to tell you how to fix the P1451 but I'm certain it's the cause of the other two codes.

P0171 - Fuel Trim System Lean Bank 1

I recommend inspecting these following areas for faults.

1. Inspect the vacuum hoses for splits, kinks,and proper connections.
2. Inspect the crankcase ventilation valve and system for leaks.
3. Inspect the fuel for contaminates
4. Inspect the PCM and sensor grounds. make sure they are clean, tight and in the proper locations.
5. Inspect the air induction system after the MAF sensor section for vacuum leaks as well
6. Inspect for engine mechanical failure.
7. Inspect the bank 1 exhaust for leaks, missing or loose exhaust hardware,
8. Inspect the bank 1 HO2S. Make sure it is installed correctly and the electrical connectors are not touching the exhaust system or ignition wires,
9. Inspect for vacuum leaks that will only affect bank 1, such as the intake manifold area, injector O rings, etc..

If you notice any faults or damaged hardware, replace it asap.

I would assume that it has no vac leaks since you took off and put back on the manifolds. I would check the mass air flow sensor to see it is dirty. If it is clean it.

what are the new codes clearing / resetting doesnt fix the problem the p0171 code has about ten different causes just changing or cleaning the sensor may not have been your problem
P0171 System Too Lean Bank 1 rescan and get all codes then look up each one most sites have causes and solutions for obd ll trouble codes