# Car Issue: Drives, But Won't Hold Idle? **URL:** \ **Category:** In My Humble Opinion\ **Created:** [February 1, 2019, 4:53pm UTC](https://boards.straightdope.com/t/car-issue-drives-but-wont-hold-idle/828793 "2019-02-01T16:53:46Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [February 1, 2019, 4:53pm UTC](https://boards.straightdope.com/t/car-issue-drives-but-wont-hold-idle/828793/1 "2019-02-01T16:53:46Z")
I have a 2002 Mazda Protege LX with about 125,000 miles. This car is typically only driven for short trips, and I believe it had a tune-up in the last year or so. Recently, we’ve needed it as alternate transportation for longer trips. Recently…whether long or short trips…the car will run fine and then suddenly cut-off at red lights while simply at an idle. (This is without A/C and/or the front defogger on.) This seems so counter-intuitive. Why would an engine be fine with smooth rhythm just to die at red lights? What does the wisdom of the SD say about the likely cause(s) of this? …or is this a sign of a need for a tune-up regardless of what I recall? Can they pull a spark plug and tell for sure? ---
**Author:** ![kopek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kopek/32/337_2.png) [@kopek](https://boards.straightdope.com/u/kopek)\ **Post date:** [February 1, 2019, 6:17pm UTC](https://boards.straightdope.com/t/car-issue-drives-but-wont-hold-idle/828793/2 "2019-02-01T18:17:44Z")
A good mechanic can tell a lot from a plug and even more from a full tune-up. I had the same problem but with a much older car; the cause then was dirt in the line and carb. It would idle fine cold but as soon as the engine got warm it would die even though it ran smooth and silk moving. A good full clean and both were fine. Since its a newer problem and coming along with a change in use I would suspect dirt. ---
**Author:** ![Dallas\_Jones](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dallas_jones/32/3277_2.png) [@Dallas\_Jones](https://boards.straightdope.com/u/Dallas_Jones)\ **Post date:** [February 1, 2019, 6:26pm UTC](https://boards.straightdope.com/t/car-issue-drives-but-wont-hold-idle/828793/3 "2019-02-01T18:26:59Z")
Could be a lot of things. Runs fine under power but dies at an idle sounds to me like a possible vacuum leak. At least that is the next thing that I would check and rule out. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [February 1, 2019, 6:27pm UTC](https://boards.straightdope.com/t/car-issue-drives-but-wont-hold-idle/828793/4 "2019-02-01T18:27:43Z")
Is the Check Engine Light on? ---
**Author:** ![DorkVader](https://avatars.discourse-cdn.com/v4/letter/d/73ab20/32.png) [@DorkVader](https://boards.straightdope.com/u/DorkVader)\ **Post date:** [February 2, 2019, 1:22am UTC](https://boards.straightdope.com/t/car-issue-drives-but-wont-hold-idle/828793/5 "2019-02-02T01:22:25Z")
Had a 95 ford contour that did that to me at a toll booth in Chicago at 5pm. Turned out to be a pulley on the timing belt that froze and shredded the belt. At driving rpms the ecm was able to compensate, but not at idle. Soo, maybe your timing system needs a check up? ---
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [February 2, 2019, 3:32pm UTC](https://boards.straightdope.com/t/car-issue-drives-but-wont-hold-idle/828793/6 "2019-02-02T15:32:57Z")
Good thoughts, all. The engine line JUST came on, so I will have to get the code(s) read. Also, a vacuum leak may be the case…as the car had some leaks in the past. The timing system should be good with the timing belt changed in a relatively “not too long ago” timeframe in its life…but I’ll keep this in mind. And, dirt is a good thought to bear in mind, as well. I guess I’ll have to see what the mechanic says. ☹ ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [February 2, 2019, 3:53pm UTC](https://boards.straightdope.com/t/car-issue-drives-but-wont-hold-idle/828793/7 "2019-02-02T15:53:21Z")
I don’t want to hijack the thread, but I wanted to share what happened yesterday. I have a '99 Jeep Cherokee that I bought new. It has \>225,500 miles on it, and it still runs strong. Only… It’s not particularly fuel-efficient, so I’ve been driving Priuses for the past ten years. The poor Jeep is seldom used. I try to start it every so often to keep the battery charged, but not often enough to keep it reliably charged. Our driveway is only wide enough for one car, so the order is: my Prius, the wife’s RAV4, the MGB (in a ‘canopy garage’), the wife’s Tacoma (partially under the canopy), and the Jeep. While I drive the MGB as often as I can, and the Tacoma gets used occasionally for hauling, the Jeep is last in line and everything else needs to be moved to use it. Yesterday I decided I’d move it to the street so that I can give it more attention. Though it had been idled last week (or a couple of weeks ago), the battery wasn’t charged enough to start it. (I had the Jeep serviced this past Summer, and it got a new battery.) So I put the charger on it for an hour or so. ANYWAY… Normally, I turn the key and it starts. Yesterday it cranked well, but didn’t catch. I had to go to the driver’s side, get in, and hold the accelerator to about 1,500 rpm to make it run, and hold the idle until it was close to its normal operating temperature. The Jeep has _always_ started right up (with a charged battery) and idled, and it has _never_ failed to continue running once started. I’m guessing that since the last time it was fueled was Summer, and since it had just under a quarter tank of gas, the cause was old fuel. After having come to near operating temperature, I moved it to the street. A little while later it was still over 100ºF on the gauge and it started right up. I drove it to the nearest gas station and put in a little fuel stabiliser and five gallons of gas, and then went to the supermarket. It operated perfectly. We’ll see how it goes today, as I’m planning to drive it to town (25 miles) for some new wiper blades. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [February 2, 2019, 6:51pm UTC](https://boards.straightdope.com/t/car-issue-drives-but-wont-hold-idle/828793/8 "2019-02-02T18:51:39Z")
> [@Jinx](#): > > …the car will run fine and then suddenly cut-off at red lights while simply at an idle. (This is without A/C and/or the front defogger on.) This seems so counter-intuitive. Why would an engine be fine with smooth rhythm just to die at red lights? Because the factors that enable it to idle are not the same as the ones that enable it to develop power and run at higher engine speeds. For example, there’s an idle control valve which needs to work properly for it to idle but which has no effect on how it runs otherwise. > [@](#): > > …is this a sign of a need for a tune-up…? No. What is nowadays referred to as a tune-up (essentially just spark plug replacement) will not help. Do not waste your money by requesting and paying for a tune-up. > [@](#): > > Can they pull a spark plug and tell for sure? No. If the engine runs fine other than at idle, spark plug inspection will shed no light on the situation. Go to a competent repair shop and describe your symptom. They’ll know what to do to diagnose the problem, and having done that what to do to fix it. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [February 2, 2019, 6:55pm UTC](https://boards.straightdope.com/t/car-issue-drives-but-wont-hold-idle/828793/9 "2019-02-02T18:55:53Z")
> [@guestchaz](#): > > Had a 95 ford contour that did that to me at a toll booth in Chicago at 5pm. Turned out to be a pulley on the timing belt that froze and shredded the belt. At driving rpms the ecm was able to compensate, but not at idle. This doesn’t make sense to me. An engine can’t run at all if the timing belt’s shredded – unless you and I define the term differently. ---
**Author:** ![DorkVader](https://avatars.discourse-cdn.com/v4/letter/d/73ab20/32.png) [@DorkVader](https://boards.straightdope.com/u/DorkVader)\ **Post date:** [February 3, 2019, 3:18am UTC](https://boards.straightdope.com/t/car-issue-drives-but-wont-hold-idle/828793/10 "2019-02-03T03:18:42Z")
The belt wasn’t totally destroyed, just mostly. There was still a bit of a strip in the center, but the edges and a bit inward were pretty well gone, shredded maybe wasn’t the most accurate description, just the one that came to mind ---
**Author:** ![Channing\_Idaho\_Banks](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/channing_idaho_banks/32/250_2.png) [@Channing\_Idaho\_Banks](https://boards.straightdope.com/u/Channing_Idaho_Banks)\ **Post date:** [February 3, 2019, 7:12am UTC](https://boards.straightdope.com/t/car-issue-drives-but-wont-hold-idle/828793/11 "2019-02-03T07:12:01Z")
Maybe it needs new spark plug wires. ---
**Author:** ![Dorjan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dorjan/32/12440_2.png) [@Dorjan](https://boards.straightdope.com/u/Dorjan)\ **Post date:** [February 4, 2019, 5:46pm UTC](https://boards.straightdope.com/t/car-issue-drives-but-wont-hold-idle/828793/12 "2019-02-04T17:46:17Z")
Based on my personal experience with a Mazda Protege where this same thing happened, your timing belt may be getting ready to shuffle it’s mortal coil. Have you had it changed within the recommended interval or have you been putting it off? ---
**Author:** ![Littleman](https://avatars.discourse-cdn.com/v4/letter/l/ccd318/32.png) [@Littleman](https://boards.straightdope.com/u/Littleman)\ **Post date:** [February 6, 2019, 1:35am UTC](https://boards.straightdope.com/t/car-issue-drives-but-wont-hold-idle/828793/13 "2019-02-06T01:35:08Z")
> [@guestchaz](#): > > The belt wasn’t totally destroyed, just mostly. There was still a bit of a strip in the center, but the edges and a bit inward were pretty well gone, shredded maybe wasn’t the most accurate description, just the one that came to mind Skipped a tooth or three. ---
**Author:** ![kopek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kopek/32/337_2.png) [@kopek](https://boards.straightdope.com/u/kopek)\ **Post date:** [February 6, 2019, 4:50am UTC](https://boards.straightdope.com/t/car-issue-drives-but-wont-hold-idle/828793/14 "2019-02-06T04:50:12Z")
**Jinx** — once you get it fixed please report back. For some reason I’m really curious now.