Re: P0171 bank 1 too lean

On 28/2/2025 11:45 am, Isaac Montara wrote:

I have a Mitsubishi Lancer ES early 2000s with a P0171 that keeps coming
back after I reset it with an OBDII hand-held code reading tool.
 I put new spark plugs in and it still sets the P0171 bank 1 too lean.
When it idles, it often kills the motor so it's not getting enough fuel I
think.
 But I don't know cars all that well. How do I increase the idle RPM on an early 2000s Lancer ES?

If you have a definite P0171 DTC, then best you determine why Bank 1 is being deemed too lean. The DTC alone is providing insufficient data - it's a diagnostic starting point, nothing more. An intake system air leak can cause such an issue so look at the intake system carefully for cracked hoses and/or loose hoses or ducting. So can partially blocked injectors. Take a look at LTFT and STFT data. Look at live data, look at freeze frame PIDs. A 20+ year old car is likely to have perished hoses and ducting and can be a PITA to locate when they become the cause of air leaks.
If you aren't familiar with OBD2 data, consult someone who is. You need to know what data is *normal* and what data is *within spec*
Dicking with the idle speed *will not fix the issue*. The idle speed is merely a symptom of idle air enleanment, not the cause.
--
Xeno
Nothing astonishes Noddy so much as common sense and plain dealing.
       (with apologies to Ralph Waldo Emerson)