1998 Subaru Outback stalls at traffic lights after driving 30 miles

Discussion in 'Subaru Outback' started by latitude xt, Nov 5, 2009.

  1. latitude xt

    latitude xt Guest

    This just started a couple of weeks ago. The car seems fine when
    driving locally, but when my husband drives it to work, or home again,
    it starts acting up. He drives about 30 miles on the highway. At
    either end, he has a fair amount of stop and go traffic. Most days
    now, the car will stall out while he's stopped at a light.

    Fortunately, it starts right up again.

    We've taken it to 2 different mechanics who cannot find anything wrong
    with it. Our own trusted mechanic, who isn't really a foreign car guy,
    ran all the computer diagnostics and said he could buy us a $500 part--
    maybe a sensor? but he didn't feel at all confident that would solve
    the problem.

    Any ideas? The Outback has about 150k miles on it.

    latitude xt, Nov 5, 2009
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  2. latitude xt

    S Guest

    Hi Emily!

    There is a air bypass thingie (technical term for when you can't
    recall the correct name ;-) (Idle Air Control valve, maybe?) that
    regulates engine idle based on coolant temperature, AC on/off, ECU
    inputs, etc. These can get sticky with fuel deposits and such over
    time, and respond slowly, or not at all.

    Symptoms would be as you describe; engine won't settle down to a
    smooth idle, or idle at all, particularly after prolonged operation at
    a fixed throttle position (highway).

    OK idle after restart could indicate a sticking condition as well.

    This is theory. 'Bout the only way I can think of to test it would be
    to replace the darned thing with a "known good" one; either new ($$$),
    or from a salvage yard. It is associated with the throttle body
    assembly, and probably will not be difficult to replace once you
    identify it; look for something on the throttle body with wiring going
    to it that _isn't_ the throttle position sensor.

    I've never seen these symptoms on a Soobie, but my old MR2 was so bad
    that I finally made a metal plate to blank the air bypass off
    entirely, as I got tired of having to drain/refill the coolant system
    to service it. (Plus MR2's aren't the most user friendly things to
    work on.)

    Maybe some one can add to this?

    Good luck; let us know what you find.

    ByeBye! S.

    Steve Jernigan KG0MB
    Laboratory Manager
    Microelectronics Research
    University of Colorado
    (719) 262-3101
    S, Nov 5, 2009
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  3. Yep, I'd say primary culprits (with no specific codes) are IAC, Engine
    Temp Sensor (not the coolant temp sender) maybe the MAF ($$$) possibly
    (least likely) intermittent Crank Angle Sensor.

    I've read you must be careful what solvent is used to clean the IAC or
    throttle body, I'd get w'ever Subaru sells for that I think.. Unless
    you want to try some do-it-yourself fixes, a good Subaru dealership
    should be able to clean, inspect or test most of these items for
    1 Lucky Texan, Nov 6, 2009
  4. Oh yeah, a car this old 'could' also have agded/cracked high voltage
    parts, plug wires and coils. But I bet the mechanics you took it too
    already ruled those out.

    Maybe someone else can think of something.

    good luck and report back when you get it fixed!
    1 Lucky Texan, Nov 6, 2009
  5. latitude xt

    latitude xt Guest

    Hmm. I just spoke to my mechanic and he says the code that came up
    indicates replacing the Mass Airflow Sensor ($500). Perhaps that's the
    "MAF ($$$)" referenced by Lucky, above? I'm worried about replacing
    very expensive parts that might not actually fix the problem. You
    know, the car just isn't worth all that much and gets lousy gas
    mileage anyway. (Although the heated seats are very nice.)

    Is it appropriate to ask my mechanic if he'd be willing to try
    cleaning the "throttle body"? I'm scared of the Subaru dealership
    because of the trauma attached to buying this car about 5 years ago.
    The sales people were very creepy.

    Thanks again for all the helpful suggestions,
    latitude xt, Nov 6, 2009
  6. latitude xt

    latitude xt Guest

    Input from hubby who drives the Subaru:

    "Usually when it stalls ALL the lights come on. But sometimes just
    the yellow "AT Oil Temp" light flashes for a bit. What I've also
    noticed is a sound coming from the front, passenger side as the car's
    slowing down, kind of like the noise a flat tire would make, or if
    there was something caught in the wheel. So it COULD be brake

    for what it's worth!

    latitude xt, Nov 6, 2009
  7. I don't always use a dealership - but in this case, they can take back
    an incorrectly installed electronic part like a MAF.
    Um, I have read of people using 'oiled'-type air filters like K&N and
    getting oil on the MAF sensor. They sometimes can clean the sensor
    with alcohol. Likely yours is bad if it's throwing a code though.

    Hey, $500 is one month's car payment for some people! hah!
    1 Lucky Texan, Nov 6, 2009
  8. latitude xt

    johninky Guest

    Usually when all the instrument panel lights come on, this is an
    indication something failed with the alternator.

    I won't buy a new MAF. Can find plenty of used for $50 or less. I
    once bought one at a yard for $5 and it is still soldiering on after 4
    johninky, Nov 6, 2009
  9. latitude xt

    Bob Bailin Guest

    What you could be hearing is sounds from the exhaust after the engine has
    stalled, but the car is still moving and driving the engine.

    One way to see if it's the IAC is to look at the throttle body and see where
    throttle stop is, i.e., the fixed area on the outside that contacts the
    movable area
    driven by the accelerator cable. If you can wedge a thin piece of something,
    a tongue depressor or even folded up paper, between the two to bump up the
    speed to about 1000-1200 rpm, that will temporarily prevent the engine from
    stalling when your foot's off the gas. Just don't make it so high that the
    car wants
    to take off on its own, or wants to slam into gear from Park.

    If that solves your problem, then clean or replace the IAC.

    Bob Bailin, Nov 7, 2009
  10. latitude xt

    S Guest

    Hi again, Emily, All!

    Poor fuel economy is another symptom that something is unhappy in the
    engine compartment. Do you know which engine is in your car? (SOHC or
    DOHC) Automatic SOHC cars of that vintage should deliver somewhere
    around 25MPG in _average_ driving (whatever that might be); the DOHC
    version a bit less.

    In any event, about the only way to address problems of this sort is
    to start replacing things until you find the problem child. We call it
    a "witch hunt" :) Lucky mentioned plug wires. I _always_ forget about
    those pesky critters. Unless you have done so in the last 20K miles,
    replace 'em. Toss on another MAF sensor. (Guys, '98 Legacy's MAF or
    MAP? Changed it somewhere in that time frame.) Put on a replacement
    IAC valve . . .

    (Acronyms. Double OverHead Cam, Single OverHead Cam, Mass Airflow
    Sensor, Manifold Absolute Pressure sensor, Idle Air Control valve . .
    .. on and on. Learn more than you ever wanted to know about it from
    Wikipedia: <http://en.wikipedia.org/wiki/Fuel_injection>)

    Emily, altho this sounds like rocket science, most of this stuff is
    easy to replace; pretty much all right on top of the engine. MAF takes
    a phillips screwdriver to undo a couple of band clamps. IAC is a
    couple of screws as well. Plug wires just take doin'. Access is easier
    if you simply remove the air intake plastic parts between the filter
    box and the throttle body; takes a 10mm socket wrench.

    Your mechanic ought to be real happy getting paid for this kind of
    stuff; clean, quick, and easy. Have him pick up a complete intake
    system from a salvage yard, and go to it. Or give the hubby a beer and
    a Craftsman tool kit, and point him at the garage. Even better, roll
    up your sleeves and DIY (won't he be surprised?).

    Our kids learned to wrench along with their drivers training (wanna
    drive it; gotta fix it . . .); the YL is quite adept at it, and held
    in awe by her boyfriend. If a 18yo college freshman (freshwoman?) can
    do a Legacy head gasket (pop sat in the shade with a beer and
    pointed), you can manage the EFI system.

    If you can't find what you need at a local yard, let me know. My buddy
    owns a Soobie/Toyota place, and I'll pull an intake the next time I'm
    down for a visit, and send it along. Probably cost around $100 +
    shipping for everything noted above, including a throttle body. I'll
    send along a complete intake manifold (has a bunch of sensors on it)
    if necessary; Bob usually aim's 'em at the scrap aluminum bin.

    ByeBye! S.

    Steve Jernigan KG0MB
    Laboratory Manager
    Microelectronics Research
    University of Colorado
    (719) 262-3101
    S, Nov 7, 2009
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