1998 Subaru Outback stalls at traffic lights after driving 30 miles

[latitude xt]

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.

Thanks,
Emily

 

[S]

Hi Emily!

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

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

 

[1 Lucky Texan]

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

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
you.

 

[1 Lucky Texan]

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
you.

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!

 

[latitude xt]

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,
Emily

 

[latitude xt]

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
related."

for what it's worth!

Emily

 

[1 Lucky Texan]

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,
Emily

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!

 

[johninky]

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
years.

 

[Bob Bailin]

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
related."

for what it's worth!

Emily

What you could be hearing is sounds from the exhaust after the engine has
already
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
the
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,
like
a tongue depressor or even folded up paper, between the two to bump up the
idle
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

 

[S]

Hi again, Emily, All!

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,
Emily

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