Trying to determine cause of low idle/stalling when damp

[ismlv]

This is going to sound bizarre, but for about the past 4 months or so,
when I first start my car in the morning and drive a few blocks and
stop (say at a stop light) at idles REALLY low (around 200RPM). If I
keep my foot lightly on the gas, it's fine. However, the other day, I
didn't and it stalled. Starts right back up with no problems and
initial start is fine.

The ONLY thing I can think of is that it happens when it sits outside.
It's a 99 SUS Ltd. Sat outside until May of last year when I moved to
a house with a garage. Bizarre as this is, at first I thought it was
the air in Hershey PA. I travel there for work and when I come out of
the hotel (generally once/week), I have this problem while driving the
few blocks to the office. Come out at lunch, it starts right up. I
know, does this sound REALLY strange?? Thought it was only when it
rained, but last few weeks, no rain, just overnite moisture I guess,
and it had these symptoms.

Yet this morning, my car sat outside all weekend in the snow and it
started up and held just fine... so maybe that blows my dampness
theory.

Anyway - I'm going to the dealer for an inspection and oil change
Friday and they're going to look in to this but thought I'd try to
solicit some input from here first.

Thanks!

 

[Carl 1 Lucky Texan]

Could be IAC (idle air control valve), when the throttle is closed it
bypasses to allow some air into the intake. It is an expensive part IIRC
but also reponds to cleaning sometimes.
Another issue with some newer cars occurs if the driver is in the habit
of slightly depressing the accelerator pedal when starting. It seems the
computer immediately records the pedal position as 'closed throttle'
assuming it is not depressed, later when the pedal has no pressure on it
the idle can be too low.
Try clearing the ECU (disconnect negative battery terminal and depress
brake pedal - wait 15-30 minutes or more, reconnect and start car (do
not depress gas pedal) and drive normally. If you still have the problem
it could be the IAC. Of course there could be fouled plugs, carbon
build-up, other problems. Do a search on IAC over at the forums on
www.usmb.net see if your symptoms match.

Carl
1 Lucky Texan

 

[pheasant]

Could be IAC (idle air control valve), when the throttle is closed it
bypasses to allow some air into the intake. It is an expensive part IIRC
but also reponds to cleaning sometimes.
Another issue with some newer cars occurs if the driver is in the habit
of slightly depressing the accelerator pedal when starting. It seems the
computer immediately records the pedal position as 'closed throttle'
assuming it is not depressed, later when the pedal has no pressure on it
the idle can be too low.

Sounds just like my kids troubles with her Dodge. It never does it to me,
and think she has a habit of foot on the gas when she starts.

The above is pasted to her windshield this morning.

Thanks Carl!!

 

[Roy Williams]

I was surprised to see your message. I have a 1998 Outback Ltd with
40k on it. During the past two months it has started doing exactly
what you describe. Initially it was when it was cold; however, now I
can get it to do it almost anytime. If I brake hard at a light and
come to a complete stop it will idle slowly, judder and often cut out.
The dealer (and they are excellent from all my previous experiences
with them) is baffled....they have worked on it for two weeks and
contacted Subaru, still no luck. Nothing shows up on their diagnostic
computers when it happens. So far we have tried replacing oxygen
sensors and speed controllers - still no luck. I wondering if the
problem stems from something that happened this summer. I was at a
light with my foot on the brake when I was rear ended at about 2-3
miles an hour - this stalled the car out. Have you found out any more?
Roy

 

[ismlv]

I had it at the dealer yesterday and of course it wouldn't do it for
them, however, I had just driven two hours from Philly back home to NE
PA to get there so it was good and warm. Anyway, they cleaned out what
they called the ISC (Idle speed control) valve. Will have to keep an
eye on it and see what happens.