Question about 1999 Subaru Forester

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Start car is fine but once hits idle speed the engine hesitates and then dies. I disconnected the mass air flow sensor and car ran better, then hooked it back up and the engine died instantly. Is this a mass air flow sensor problem or something else?

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I would agree with your diagnosis. i had a similar problem with a crown victoria. disconnecting the maf sensor made it run better. i replaed the sensor and have had no problem since

Posted on May 08, 2010

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Posted on Jan 02, 2017

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I have a 98 Nissan Frontier. It wasn't running right so I unplugged the maf sensor and it ran better. I bought a new one from eBay. Replaced it and now it's running worse than before


    What Are the Symptoms of a Faulty Mass Air Flow Sensor?
    • The engine stalls soon after starting.
    • The engine drags or hesitates when idle or under load.
    • The engine hesitates and jerks during acceleration.
    • The engine hiccups.
    • The engine displays unusually lean or rich idling.

    Mass Airflow Sensor: An Easy Fix for Big Problems from a ...

    www.airtexproducts.com/news-blog-mass-airflow-sensor-an-easy-fix-for-bi...

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Idling rough and hesitating when accelerating


This sounds like the mass airflow sensor.

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My truck wont start unless i prime the carborator first, then it wont stay running unless i rev it high just before i put it in gear, or im accellerating...


To start with, you have a throttle body instead of a carburetor.
On that throttle body is a component called an air control valve.
That valve is how the computer controls the idle speed. It should open and close the air flow into the intake manifold as needed.
Is the check engine light on when you are driving ? Have you checked the fuel pressure ?

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My 97 jimmy sometimes dies while driving and idling. no lights come on, fuel pump is working, is not overheating. once it dies, it starts up again immediately.


Here is the common cause of surges, stalls at stops, slow idle speed, erratic idle speed, rough idle and engine hesitation (and other problems), it is in most cases the idle speed control air-bypass valve and or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.

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1996 Ford Taurus power hesitation


If you disconnected the Mass air flow sensor the car should have die out at idle. Check fuel pump pressure at the fuel rail should be 30 psi at idle. Low fuel pressure will cause your po 171, 172, problems which could cause the other to problems. You might be needing a fuel pump and filter.

Jun 24, 2009 | 1996 Ford Taurus

1 Answer

Car sputters or dies when idling, but starts fine.


I suspect you have an idle circuit issue. When the thottle is closed, the throttle valve is almost closed (like 95%). The linkage on the throttle body is against the hard stop.
SO, when idling you need a way to let enough air into the engine to maintain an idle speed. The IAC, Idle Air Control valve is the way you do that and the engine computer controls the rate of air flow.
Sometimes it gets plugged up so you can clean it with a little carb cleaner. Might have to take it apart.
Also, you have a MAF, Mass Air Flow sensor that tells the computer how much air is flowing through the air cleaner intake at any time. The sensor gets coated with varnish and vies a false reading. Clean it gently with carb cleaner and a toothbrush.
Other than that, I would go to an auto parts store that can run a computer scan for free to see if you have any fault codes stored. They will tell you next stpes.

I assume you 2.0L SPI engine & not Zetec.


Idle Air Control (IAC) Valve —2.0L SPI Removal
  1. Disconnect the idle air control (IAC) valve electrical connector (air cleaner outlet tube removed for clarity).
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  1. Remove the IAC valve.
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  1. Remove and discard the IAC valve gasket.
cdecc8a.gif Mass Air Flow (MAF) Sensor Removal
  1. Remove the air cleaner outlet pipe.
  1. Disconnect the mass air flow (MAF) sensor electrical connector.
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  1. Remove the MAF sensor.
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clean element inside carefully


PS. A good running engine makes for a better running transmission

Mar 02, 2009 | 2003 Ford Focus

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2000 Contour dies at low idle


you could try to clean the mass air flow sensor

Oct 23, 2008 | 2000 Ford Contour

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Buick lesabre nightmare 2


  • The PCM doesn't even see the O2 sensor until engine temp has reached operating temp,the vehicle goes from open loop when cold,to closed loop when warm,where the PCM uses the O2 sensor to measure the rich/lean of the exhaust content,and from that,adjust fuel richness to achieve 14.7 to 1 air/fuel ratio.So when cold,the O2 sensor is out of the picture anyways.When unplugging sensors,it can be deceitful.The PCM has a program whereas,if a critical sensor (such as the mass air flow) is somehow damaged and out of the picture,the PCM will substitue a generic value that will allow the engine to stay running.So,by unplugging the MAF,it did try to run on it's own better than plugged in,there's the problem area.The vehicle is running better with the MAF unplugged,because the MAF is likely bad,and the PCM is substituting it's generic value when it IS unplugged.Something to recheckThe PROM update is a newer program for the PCM,and likely won't fix it unless the PCM is bad.I would try a good used PCM as a last or later resort,because i have seen my fair share of defective PCM's too.I have taken some PCM's apart,and found capacitors that had gone bad and leaked all over the circuit board,mostly Honda and Mitsubishi and Chrysler though.Good luck,keep me posted.

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