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Car stalling while idling in cold weather

Hello, I have been driving my 1998 STS for 3 years now and have been having an issue with stalls for the last 18 months. When I pull up to stop lights occasionally the engine will stall out. This generally happens in cold weather most often. Generally if it stalls once on a drive it will then stall at nearly every stop unless I give it some gas. When it stalls, the battery and oil lights come on.

Edit: A few other symptoms that I had neglected to mention:

Car stutters a little right before it stalls. Drops from around 1000 RPMs to 500 then back up and then stalls.

Car has only stalled once in last 4 months after not running for 10 days. This is what convinced me it had something to do with weather, as once temperatures where consistently above 50 degrees F the problem seemed to disappear.

Car never stutters or stalls if the accelerator is even barely pressed
I have replaced the battery and was informed it may be an alternator issue. Any help would be greatly appreciated.

The person that told you it may be an alternator issue… did he test the battery and charging system? Was he a qualified mechanic, or just a friend? Or a parts-counter (or skippy-lube) kid?
Has anything else been checked and/or tested by a qualified diagnostician?
Has any work been done on the vehicle just prior to the problems?

It’s a 1998, 19 years old. The possibilities include but are not limited to
1 poor compression
2 worn out spark plugs
3 a bad Idle Air Controller
4 a weak fuel pump
5 a bad temp sensor
6 a vacuum leak
7 a valve problem (weak springs, bad lash, burned valves, and on and on)
8 (some) weak coil(s) (I’m not sure how your ignition system is set up)

The bottom line is that someone is going to have to look at this hands-on and perform some diagnostic tests. If it were me I’d probably start with a test of the battery and charging system followed by a compression test. I’d also want to “read” the sparkplugs (they can be highly revealing), and maybe check the vacuum stability. That’s just for starters.

More than likely the problem is with Idle Air Control valve.

https://www.rockauto.com/en/moreinfo.php?pk=86746&cc=1313843&jsn=406

The IAC valve is what controls the engines’ idle whenever the accelerator is released.

One way to determine if there’s a problem with IAC valve is, you’re able to prevent the engine from stalling if you slightly tip into the throttle while sitting at a stop.

Tester

3 Likes

The person who introduced the alternator theory is just a personal dabbler in mechanic work. So I didn’t want to jump straight to it without inquiring elsewhere. I had the battery checked and replaced by a qualified technician 9 months ago. Spark plugs have also been replaced a few months prior to that. I hadn’t taken the car back in since the battery was replaced as I haven’t had the money or time.

A few other symptoms that I had neglected to mention:

Car stutters a little right before it stalls. Drops from around 1000 RPMs to 500 then back up and then stalls.

Car has only stalled once in last 4 months after not running for 10 days. This is what convinced me it had something to do with weather, as once temperatures where consistently above 50 degrees F the problem seemed to disappear.

Car never stutters or stalls if the accelerator is even barely pressed.

Sure sounds like and idle air control to me, too. An OEM AC Delco part is $75 on RockAuto. It could be buildup in the idle air control passages, too.