How JustAnswer Works:

  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.

Ask TECH1994 Your Own Question

TECH1994
TECH1994, Technician
Category: Car
Satisfied Customers: 88
Experience:  10 YEARS TECHNICIAN EXPERIENCE
Type Your Car Question Here...
TECH1994 is online now
A new question is answered every 9 seconds

2001 Mercury Sable: lean..MAF sensor..The PCV elbow hose..fuel filter

Resolved Question:

My 2001 Mercury Sable 3.0L is giving lean codes on both banks - P0171 and P0174. I have replaced 3 parts. They are the MAF sensor, The PCV elbow hose (which had a huge leak in it), and now the fuel filter. It stumbles on the road as well as the interstate. It is doing something really strange now. In park, The idle cycles in repetition from 1600 RPM down to about 600 and then back to 1600 and then it repeats like a metronome. It just cycles back and forth but the engine dies when I put it in gear. It stalls at red lights unless I keep it highly revved up about 1600 - 2000 RPM.
When the battery cable is first connected, it seems to run perfectly for about 20 minutes or so and then it just goes crazy. What could this be?
Submitted: 6 years ago.
Category: Car
Expert:  TECH1994 replied 6 years ago.

Hello, welcome to just answer

Here is what each code means

Code P0174 = Engine started, engine running at cruise speed for 3 to 4 minutes, and the PCM detected the Bank 2 Adaptive Fuel Control System reached its rich correction limit (a lean A/F condition).

Code P0171 = Engine started, engine running at cruise speed for 3 to 4 minutes, and the PCM detected the Bank 1 Adaptive Fuel Control System reached its rich correction limit (a lean A/F condition).

Here is a list of possible causes to set these and cause the symptoms you are having

  • Air leaks after the MAF sensor, or leaks in the PCV system
  • Exhaust leaks before or near where the HO2S is mounted
  • Fuel injector(s) restricted or not supplying enough fuel
  • Fuel pump not supplying enough fuel during high fuel demand conditions
  • Leaking EGR gasket, or leaking EGR valve diaphragm
  • MAF sensor dirty (causes PCM to underestimate airflow)
  • Vehicle running out of fuel or engine oil dip stick not seated
  • Carefully inspect the following areas for potential air leaks:

    • Hoses connecting to MAF

    • Hoses connecting to throttle body

    • Intake manifold gasket leaks

    • PCV disconnected

    • Vacuum lines disconnected

    • Improperly seated dip stick and tube

    • Exhaust leaks at flanges and gaskets

    If any problems are found and you repair them, then clear codes and unhook negative battery cable for approximately 2 minutes. Reconnect negative battery cable and start vehicle to let computer relearn idle.

    The reason it is okay for about 20 minutes after hooking up battery is because vehicle is running in open loop and does not care what the oxygen sensors are saying. It delivers a predetermined amount of fuel to engine until operating temperature comes up. Once up to operating temperature it goes to closed loop and now you have problems because it takes inputs from all sensors to make fuel adjustments and with a bad vacuum leak persay it will cause the problem you are having and cause those codes to set.

    TECH1994, Technician
    Category: Car
    Satisfied Customers: 88
    Experience: 10 YEARS TECHNICIAN EXPERIENCE
    TECH1994 and 15 other Car Specialists are ready to help you
    Customer: replied 6 years ago.
    Reply to TECH1994's Post: One thing I forgot to mention is that fuel consumption has increased but I can't find any fuel leaks externally. What does this mean?
    What is the best way to find vacuum leaks?
    Also, what does it mean when the engine at idle cycles between 1600 RPM and then back down to 600 and then 1600, then 600, and it just repeats up and down, up and down like that, then it dies when i place it in gear? What does that indicate?
    Customer: replied 6 years ago.
    But if it was an exhaust leak before or at the o2 sensor, wouldn't that only give a bank 1 or bank 2 error and not both? I am receiving both 171 and 174.
    Expert:  TECH1994 replied 6 years ago.
    Yes fuel consumption will increase with vaccum leaks. Also the engine will idle erratically and rpms go up and down and vehicle can die with put in gear. Everything you have mentioned indicates a problem or vacuum leak in one of the above areas I mentioned. The best way to check for vacuum leaks that I prefer is to spray carb cleaner around intake very carefully and vacuum lines. If idle changes then there is your problem. You could also try water in a spray bottle but I find the carb cleaner more successful or brake cleaner. However, be extremely careful when doing this as if it hits an open spark it could ignite. I would go as far really to recommend you letting a qualified shop perform these tests. The labor to check for these leaks should not be anymore than an hours labor.
    Customer: replied 6 years ago.
    Yes I also think it is a vacuum leak. Your advice has been helpful. Thank you.
    Expert:  TECH1994 replied 6 years ago.

    Good luck, if you need anything in the future you can always request me or speak to another just answer expert.

    Thank You

    JustAnswer in the News:

     
     
     
    Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
    JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
    Web sites like justanswer.com/legal
    ...leave nothing to chance.
    Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
    Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
    I will tell you that...the things you have to go through to be an Expert are quite rigorous.
     
     
     

    What Customers are Saying:

     
     
     
    • I would (and have) recommend your site to others I was quite satisfied with the quality of the information received, the professional with whom I interacted, and the quick response time. Thanks, and be sure that I'll be back whenever I need a question answered in a hurry. Stephanie P Elm City, NC
    < Last | Next >
    • I would (and have) recommend your site to others I was quite satisfied with the quality of the information received, the professional with whom I interacted, and the quick response time. Thanks, and be sure that I'll be back whenever I need a question answered in a hurry. Stephanie P Elm City, NC
    • used your service this weekend with "Trecers" help. thank you ,thank you, thank you. replaced an A/C fan motor. Local Auto Zone had part. $15.00 "tracer" fee and $40.00 for parts, I saved several hundreds of dollers at a shop. i will recommend you and use you in the future. David L. Richmond, TX
    • 9 dollars, 2 hours of my time, and I drove away. Your diagnosis was right on the mark. Thank you so much. Phil Marysville, CA
    • Lurch. Thank you very much. I had real doubts about this website but your promptness of response, quick followup and to the point answer with picture was incredible. Charles Walnut Creek, CA
    • As a single woman, I really appreciate an excellent and affordable opinion.
      Thank you Geordie, I will not hesitate to contact justanswer in the future!
      Sue Charleston, WV
    • Another great insight to what may be the problem. I will have my mechanic take a look at it tomorrow. Thanks again, Frank...you do indeed know your stuff. Jim Castleberry, FL
    • The nearest Volvo dealer is 160 miles away. Best $15 bucks I have spent in a long time! Paul M Corpus Christi, TX
     
     
     

    Meet The Experts:

     
     
     
    • Chris (aka-Moose)

      Technician

      Satisfied Customers:

      846
      16 years of experience
    < Last | Next >
    • http://ww2.justanswer.com/uploads/MU/muddyford/2012-6-13_1204_1.64x64.png Chris (aka-Moose)'s Avatar

      Chris (aka-Moose)

      Technician

      Satisfied Customers:

      846
      16 years of experience
    • http://ww2.justanswer.com/uploads/TE/TedG/2012-6-15_14759_avaLarge.64x64.jpg Ted G.'s Avatar

      Ted G.

      ASE Certified Technician

      Satisfied Customers:

      1596
      20 years auto repair experience, ASE Master Tech, Mechanical Failure consultant, Expert Witness
    • http://ww2.justanswer.com/uploads/joecamel90/2008-11-13_03615_head_shot.jpg George H.'s Avatar

      George H.

      ASE Certified Technician

      Satisfied Customers:

      1311
      ASE Master Tech 15+ yrs, AAS Automotive Technology, Factory trained Asian specialist
    • http://ww2.justanswer.com/uploads/AM/amedee/2013-10-24_23656_Amedee1.64x64.jpg Amedee's Avatar

      Amedee

      ASE Master Tech

      Satisfied Customers:

      2367
      ASE Master Tech advanced level specialist
    • http://ww2.justanswer.com/uploads/SU/supermechanic/2013-8-23_03546_500.64x64.jpg Jerry's Avatar

      Jerry

      Master Mechanic

      Satisfied Customers:

      1906
      ASE master, 30+ years. All makes and models. Trouble shooter, shop forman, service manager
    • http://ww2.justanswer.com/uploads/CR/crzydrvr00/2013-11-3_12123_246347.64x64.jpg Richard's Avatar

      Richard

      ASE Certified Technician

      Satisfied Customers:

      942
      12 years Ford Lincoln/Mercury Jaguar dealership as a technician and shop foreman reparing all makes
    • http://ww2.justanswer.com/uploads/ST/Steve7654/2012-6-5_215929_japic800x660.64x64.jpg Steve's Avatar

      Steve

      Auto Service Technician

      Satisfied Customers:

      1980
      25+ yrs experience as a professional working technician; ASE L1 master technician