GenVibe - Community for Pontiac Vibe Enthusiasts

Hi, everyone. Happy holiday!

My 05 Base got the P0171 code again. The temperature has been around 34 F recently. When the engine is started, the STFT will gradually go up to +20% while the engine idling around 2000 rpm. Several minutes later, the engine speed drops to 900 rpm and the STFT goes down to -5%.

I have clean the mass airflow sensor and throttle body, changed the PCV valve, and inspected the PCV hose recently. I am going to change the intake manifold gusket. I haven't checked the two oxygen sensors yet.

Is there anyone kind enough to explain the mechanical reason behind my observation? Thank you very much.

When the engine is cold it needs more fuel, that's why it's adding 20% more when it's cold and
at 2000rpms. That sounds a little high to me. but the -5% means it has to much fuel and it's taking
some out. But -5% isn't even that bad.......

Typically the code P0171 is set when either short term fuel trim (STFT) or long term fuel trim (LTFT) adjustment exceeds a certain value (usually +25%).

You probably have a vacuum leak somewhere. Check all the hoses on your intake. Or spray down your intake / intake manifold / and
other hoses with WD40 and see if your RPMS go up if they do that's where your leak is.