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From: AMuzi <am@yellowjersey.org>
Newsgroups: alt.home.repair,rec.autos.tech
Subject: Re: P0171 bank 1 too lean
Date: Thu, 27 Feb 2025 20:01:31 -0600
Organization: Yellow Jersey, Ltd.
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On 2/27/2025 6:45 PM, 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?

This guy covered the usual items for 'lean bank'

PCM software needs to be updated
Vacuum leaks (Intake Manifold Gaskets, vacuum hoses, PCV 
hoses, etc.)
Mass Airflow Sensor (MAF)
Plugged Fuel Filter or weak Fuel Pump
Plugged or dirty Fuel Injectors

without success but then discovered an unusual failure:

https://www.clublexus.com/forums/rx-2nd-gen-2004-2009/671879-finally-solved-p0171-and-p0174-codes.html

-- 
Andrew Muzi
am@yellowjersey.org
Open every day since 1 April, 1971