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From: Xeno <xenolith@optusnet.com.au>
Newsgroups: alt.home.repair,rec.autos.tech
Subject: Re: P0171 bank 1 too lean
Date: Sat, 1 Mar 2025 11:36:56 +1100
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On 28/2/2025 1:01 pm, AMuzi wrote:
> 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
> 
Interesting story and there are many like this. But the dealer scan 
tools should have been able to test for it. Look up OBD2 Mode $08 - 
control operations of on-board systems. Mode $08 allows the tech to 
control certain operations of the EMS allowing a scan tool to do 
bidirectional control of an onboard system or test. Most solenoids and 
emission equipment can be controlled and cycled independently of 
conditions and commands. Factory scan tools and the more expensive 
aftermarket scanners offer bi-directional functionality thus have Mode 
$08 capabilities. This is a very handy method of testing for equipment 
failure without the need to wait for the EMS to command the operation. 
Would have been very handy for you, no need to wait out the time or an 
idle situation.

HTH

-- 
Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
       (with apologies to Ralph Waldo Emerson)