Hi all. Looking for some help with a consistent P171 code. I changed my oil, air filter, new plugs. When I changed the air filter the tube to the throttle body was loose so i tightened it hoping that would work. It didn't. It is consistent to when it appears. I can clear the code and drive 400 miles on the Interstate at highway speeds without issue. The code only appears when I am starting the car or idling at a stop sign, and even then not every time I start the car or every time I am stopped. I do notice a slight roughness in the engine when it occurs. Initially the "restricted performance appears but that clears within about 1 minute of driving at normal speeds. I checked my vacuum lines and they all appear to be ok. Any help you can provide would be appreciated.

 

You are only getting the one code P0171 and not P0174 along with it? I would see about adding a can of BG44K to the fuel and see if it clears. This code is telling you that you have a lean fuel mixture on “A” bank that can be caused by many things. I suggest you try the fuel additive and see what takes place. Do you know when the plugs have been replaced?

Engine misfire
Air intake leak between MAFS and throttle
Fuel filter, system blockage
Fuel injector blockage
Fuel pressure regulator failure
(low fuel pressure)
Low fuel pump output
HO2S harness wiring condition fault
Exhaust leak (before catalyst)
ECM receiving incorrect signal from one
or more of the following components:
ECTS, MAFS, IATS, TPS

 

Hey Gus. I just changed the plugs before I drove it from Wisconsin to Florida, and it was throwing the code before I left. I cleaned out the mafs when I changed the air filter. No other codes, just the 171. And only at idle or at start up. I dorve it 300-400 miles between stops on the way down. When I fueled and started the car, the code would appear. I cleared the code, started up again and it didn't have the cel on, and drove it to the next stop. No missing-ran smooth, and no code until the next fuel stop. Thanks

 

A single bank lean generally seems to end up as either an inlet manifold leak or a bad O2 sensor.
There are lots of threads on diagnosing both problems.
You will need, for preference, a reader giving live data.
The inlet leak can be diagnosed by watching STFT on bank 1 and spraying carb cleaner or an unlit propane torch. If there's a leak you will see the STFT drop when you're near the leak.
You CAN test O2 sensors but most people seem to suggest swapping them (not easy to get them out).If the fault swaps banks - new sensor time.
At your mileage it could be a sensor problem.

 

Or bank B is close behind...live monitoring of the trims will tell all.