1998 Subaru Outback stalls at traffic lights after driving 30 miles

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.



“Foreign car guy.” That’s one I haven’t heard in a long time.

How can a mechanic stay in business and not know anything about “foreign” cars? I don’t see how they are any different. All modern cars use electronic engine management systems, and they all hook up to the same OBDII diagnostic computer. Besides, your Outback was probably built in Indiana. How “foreign” is that?

Has the Check Engine Light ever come on when the car stalls? If not, a computer diagnostic won’t reveal anything.

Idle speed is controlled by the Idle Air Control (IAC) valve (just like a Ford or Chevy) and its associated parts. If the valve is dirty or sticking it can cause incorrect idle speed or stalling.

Vacuum leaks can also be a source of idle problems.

Do you know which sensor the mechanic suggested? Was it, perhaps, a throttle position sensor?

I take it back about the “foreign car guy”… sorry; didn’t realize that no longer makes a difference. I’m mechanically ignorant and probably still using my dad’s 1940s ideas.

The code that my mechanic saw indicates replacement of the Mass Airflow Sensor, a $500 part. Are there other tests or cheaper repairs that should be attempted before going this route?

Is there a danger in just driving the car as usual and restarting it every time it stalls? Thanks again,