Car accelerating on its own

twinklenoseJune 29, 2005

Hi! First time poster here and am sure hoping you can help....

This morning a very strange and scary thing happened. Less than ten minutes after leaving home, we were driving down the highway, where the speed limit is 70, when suddenly something didn't feel 'right' and I noticed the car was going that fast without my foot even touching the accelerator--it felt like cruise control racing up a hill, only we weren't on an incline, and my car doesn't feature cruise control!--and it didn't seem to want to slow when the brake was applied. In desperation I pushed on the brake pedal hard as it would go, pulled the emergency brake, and got onto the roadside, where I shoved the gear into Park.

I got out and checked that the mats nor anything else were interfering with the accelerator, and when I tried jiggling it, it felt normal.

Hoping it was merely a very weird fluke, we proceeded on our way, and about 10 minutes later the very same thing happened. Only this time it was more difficult to stop, and when thrown into Park, the motor surged loudly and died.

Our mechanic came soon thereafter and checked that cable under the hood that operates the gas. At first he suspected the cable might be fraying and catching, but he checked, and that was fine. He sprayed it with WD-40, and couldn't find anything wrong, so he followed me all the way back home, and of course then the car handled perfectly!

He did caution me, though, that in the event it happens again, to switch the key off and put it into neutral and veer carefully off the road.

Now I'm afraid to drive it, though. Luckily, this occurred on a rural highway. It would've been awful to be in town, surrounded by other vehicles and maybe even people!

I just don't understand it. Plenty of times I've had other cars die on me, but never one try to run off!

By the way, it's a '99 Mercury Tracer.

Thank you for listening!


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Sounds like your pedal stuck.Did you look to see ifrug or anything else may have gotten under pedal,had it happen once

    Bookmark   June 30, 2005 at 7:45AM
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Sometimes the idle air control valve will stick. It's a $50 part that takes about 5 minutes to replace.

    Bookmark   June 30, 2005 at 10:24AM
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Thank you both so much for answering.
Yes, Bulldinkie, that's the first thing that crossed my mind as well, but nothing was in the way.
Brian, I'll ask my mechanic to check for that part. Thanks!
I was beginning to wonder if the car hadn't become possessed, or maybe it was 'mad' at me, or showing off, since we just got it paid for!:)

    Bookmark   June 30, 2005 at 7:39PM
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Twinkle, do not drive that car til you get it fixed.
A terrible thing happened here in my town.
A man was driving into a tire place to have his tires checked.
His car did what your's did and he couldn't stop it.
He ran over a customer cutting off both his legs.
It was awful.
Please be careful.

    Bookmark   June 30, 2005 at 9:31PM
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Oh, my gosh, Janis!!--I was nervous enough before, so am certainly taking your advice to heart! Thank you for posting such a concerned warning!

    Bookmark   June 30, 2005 at 10:15PM
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Posted by: brianl703 (My Page) on Thu, Jun 30, 05 at 10:24

Sometimes the idle air control valve will stick. It's a $50 part that takes about 5 minutes to replace.

It should take about an hour( or more) to do a proper diagnosis, and this must be done to assure that indeed it is an idle air control problem and not something else..

It is not cost-effective nor safe to guess, no matter how likely !

I wonder if the engineers at the car-makers test these devices - to make them fail safe as possible and repairable...Also, very important, is to establish diagnostic procedures that are effective and economically feasible...

    Bookmark   July 1, 2005 at 2:01PM
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Back in the 80s or 90s, the Audis were doing this, and I do not,as yet, know exactly why..
And since human life is at stake, it behooves us to know , scientifically, exactly WHY !!
No question, IMO, some people panic and hit the gas by mistake when they wish to brake...
This may be impossible to solve

    Bookmark   July 1, 2005 at 2:11PM
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The symptoms the car is exhibiting could only be caused by additional air being admitted into the intake manifold.

There are three ways this can happen:

1)The throttle butterfly is open.

2)The idle air control valve is open.

3)There is a vacuum leak.

#1 would seem to have been eliminated as the cause of the problem by the checks that the mechanic did.

#3 would also seem to have been eliminated as the cause of the problem by those checks. As well, a vacuum leak large enough to cause the engine to accelerate on it's own would cause serious drivability problems (I'm talking bucking-bronco type serious) and would turn on the check engine light.

So we are left with #2, which seems as the most likely cause of the problem because in both reported instances it happened after an operating condition where the idle air control valve was being commanded fully-open by the computer.

    Bookmark   July 1, 2005 at 2:25PM
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Brian--I found a drawing of this valve online. Could you please tell me approximately where on the engine the real thing might be located? Is it usually easy to reach?

...And just wondering, but is this something a novice could easily replace? I've replaced a fuel filter before (different car).

Thanks again--

    Bookmark   July 1, 2005 at 9:49PM
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It'll be located on the throttle body, which is where the throttle cable is attached, along with the air intake duct from the air filter.

Yes, a novice could certainly replace this part. On the Escort/Tracer, there isn't anything in the way that I can recall.

    Bookmark   July 1, 2005 at 11:28PM
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I am not an ASME member of anything, but the idle air valve, or idle stabilizer valve passes a very small amount of air, barely enough to stabilize the engine at idle. It may even be cut out of the circuit at anything over idle speed.

You seem to have another problem, possibly to do with the engine control unit, the computer.

As to the Audi "runaway acceleration", the TV crew had to gimmick the car, similar to the Chevy truck fireball scene to reproduce it so they could dramatically show how evil the cars were. It appears that the culprit was gas and brake pedals set more closely together than on the typical US car. People were pressing the accelerator and swore they were STANDING on the brake.

Bought my first Audi at 10 cents on the dollar because they were so undesireable in those years, still driving them.

You DO have a serious problem.

Has anyone worked on the transmission in the recent past?

There was a case of a bolt put back in backwards in a tranny rebuild, where the threaded end of the bolt stuck up too far and interfered with the accelerator linkage and locked the car in full throttle.

Good luck with the problem. Now that it's paid off, mebbe you should get rid of it.



    Bookmark   July 10, 2005 at 12:01AM
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I am aware of at least one reported instance of a faulty idle air control valve causing the vehicle to accelerate on it's own. The specific case I recall involved a Ford Taurus and happened after the idle air control valve was cleaned. (Ford doesn't recommend cleaning them--maybe that's why.).

It definitely is not cut out of the circuit above idle. Above idle, on Ford vehicles, it is fully open so that the computer can gradually close it so as to provide smoother deceleration if the driver lifts completely off the gas pedal.

    Bookmark   July 10, 2005 at 1:04PM
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I was over my sisters apt and was sitting in my car, my car was in neutral with the emergency brake on, I have a 5 speed, Kia Spectra. THe car was in idle started to accelerate on its own, I turned my car off and restarted and it was ok for about 2 minutes then it did it again and I repeated the turning of the engine off then back on, at that time the check engine light came on. I got brave and drove it home and the check engine light remained on. A couple of days later I was going 70 mph my crusing speed,(I don't have cruise control) as I was traveling on 265 my car started to accelerate on its own, it kind of scared me at first because I was up to 82 mph, at that time I merged into the righthand lane I engaged my clutch and put the stick in neutral and turned the car off and then restarted it. It seemed to be ok because it did not do it again. The next day it was dropped off at the Kia store. I had it in the shop before for this problem, and they adjusted the throttle cable, Can anyone help me with this because the shop gave the car back to me and sad that there is nothing wrong and it didn't act up on them. I know something if wrong with this care. I dropped the car off again today. Any suggestions that I can pass on to the Kia place to try. I'm getting very leary of driving this car. Thank you for any suggestions......

    Bookmark   November 13, 2006 at 9:40PM
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My BMW 5 series is doing the same thing at moment. I have it sitting idle and then the car starts to accelerate on it's own as sson as I put power in and take foot off pedal. Accelerates from 700rpm to 5500rpm in less than one second. MMmmmmmm.

    Bookmark   December 9, 2010 at 7:00PM
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I have a 2000 Toyota Echo....Just bought it and of course as soon as i get it home, it started acting up! THere is no cruise.
When its in park it's starts reving and wont stop unless i turn it off or sometimes when I press the gas and Rev it myself. When Im driving it acclerates by its self. I could drive for miles going 40 with out touching the gas.
When im going 100 it will slow down to 60 or 50 when my foot is off the gas but then it will stick at those speeds and not slow down.
It will always come to a stop when i press the brake.
When im stoped at a stop sings or lights it's so eager to go....It's like it has a mind of it's own, it dosen't like to be still.
What could this problem be....

    Bookmark   April 23, 2011 at 5:46PM
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I see that this was posted a while ago, but I thought I'd ask if you have gotten this problem fixed. I have been having the same issue with my 99 Honda Passport. At least 5 mechanics have looked at it and cannot figure out the problem. All of the causes listed by other people here have been checked out and parts replaced but it still acts the same. Let me know if you have figured out what's wrong with your car.

    Bookmark   August 23, 2011 at 12:38PM
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I seam to be having the same problem with my 2003 Impala, i as well have checked all those things and we still cant find out what's wrong with it, but i did notice that if u disconnect the MAP sensor it stops doing it. So i replaced it and it keeps doing the same thing... So lm certain that it has to do with a sensor or something, but if i find out the problem first ill post it cuz i know its stressful situation and expensive to be guessing and buying parts that aren't it...

    Bookmark   August 19, 2012 at 11:13PM
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This could have something to do with the recent potential Ford recall of Sable/Taurus? Maybe Tracer will be involved as well. The recall is concerning stuck accelerator mechanisms.

    Bookmark   October 27, 2012 at 12:07PM
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This problem has been resolved with certainty on one car I've travelled in as passenger.

The valves of the cylinder head were staying partially open (a very tiny amount). This causes compression and combustion leaks up the inlet valve side, into the fresh air inlet manifold and increases the air pressure there. The sensors (often called MAP) are partly responsable for the conclusion in the motor computer that the airflow is suddenly more free, as if the driver has fully opened the throttle letting a lot more air into the manifold. The MAP value is used in the computer to seek a proper mixture (along with oxygen sensor and other temperature measurements). To get optimum mixture with what the computer thinks is now very much air . . . . it injects more fuel immediately and far more than the idle speed value. Result . . . the car accelerates on its own, no matter what you do with the throttle position.

Solution. You may have a car with hydraulic tappets or used to. Many newer models are going back to manual adjust tappet clearances. If that's confirmed good then sticky valves (dry or overheating) need be investigated. If you use very clean petrols or LPG Liquified Gas they often lack the oiliness that helps valve function and with LPG due to hot, lean combustion the valves can wear drastically and recess far more than usual into the cylinder head or have uneven wear.

So, it's tappets and valves and that's why the problem doesn't show up on diagnostics nor is it always going to occur and if you stop the vehicle before inspection . . . the problem may have disappeared. Computers, lambda sensors, throttle bodies, cables, electronics and everything else a technician can change out . . . are usually in good working order. It's a mechanical problem in the steelwork of the engine.

Disconnecting the MAP can work to get around or get home. In the case of Daewoo that works because the engine computer switches immediately to TP mode (Throttle Position mode). It may not be so precise in power, may stall or idle rough, may have emissions outside the regulations yet it can stop this particular cause of sudden accelerations. It's a legitimate mode for driving yet may cause long term problems to oxygen sensors and other parts expecting a more precise mixture of air to fuel. I'm unaware of the effect of disconnecting the MAP on other makes and models of cars.

    Bookmark   January 2, 2013 at 10:21AM
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The engine needs more than just air, it needs extra fuel as well, otherwise it will run lean. More fuel is only added when the throttle cable is operated.

The Echo sounds like a vacuum problem ; there is a leak, possibly in the air intake, and the computer compensates for the lack of vacuum by opening the butterfly valve, rather than using the idle circuit when idling.

The Tracer is a Mazda, and unrelated to the Taurus. The recent Toyota recall was for a plastic accelerator pedal that lacked a nylon bushing (to "save" money) and so would "stick" on the mould line of the two parts of the pedal.
Once the engine starting running flat out, the transmission selector could not move because the high fluid pressure prevented the spool valves in the control block from shifting, and the brakes were ineffective (normally, the transmission will slip into neutral when the brakes are applied, but the high fluid pressure prevented this).

    Bookmark   January 10, 2013 at 1:14AM
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I have a 2005 Grand Am V6 with 177k miles. It has the following symptoms:

--"stuttering" when accelerating from a complete stop. Worsens after highway driving. Has been occurring for over 2 years.

-- at highway speeds, revs up from 1800rpm to 2200rpm, then back down to 1800rpm repeatedly. This does not occur when driving the vehicle in 3rd gear. It has been happening for about 1 week and getting worse.

--engine frequently revs up to 1600rpm when in "park" and goes down to 900rpm in "drive." This started yesterday.

--engine frequently accelerates by itself or maintains speed with foot off gas pedal while driving between 20-60mph, and is ready to jump off the line after a stop. This began yesterday.

--Restarting the engine temporarily stops the revving while in park.

Any ideas will be greatly appreciated! I just want to know what I might be looking at before taking it in to the shop :) Thank you, Kristine

    Bookmark   June 14, 2013 at 1:39AM
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I drive a 2002 Hyundai Elantra 5 speed standard.
When i bought the car it was in great condition, about 6 months after it started surging on me when i was in neutral and would go from about 700RPM to about 5000RPM and then drop and spike repeatedly. I drove it for a while, had a bad clutch on the car so id just leave it in gear and with my foot barely on the clutch it would idle at about 700RPM like normal. A few months after that it stopped spiking and just would climb from 700 up to 5500 when idling. I just got a brand new clutch installed in my car and obviously my cheat way of getting it to stop is absolutely not an option anymore. Anyone have any idea what it could be? Vacuum leak crossed my mind as the head gasket needs to be replaced. Checked the throttle cable. I literally have to turn my car off at lights if i need to drive anywhere! and who wants to do that?! I need some help to get this diagnosed so i can fix it as soon as possible.

    Bookmark   November 18, 2014 at 12:26AM
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If your vehicle is beta1 1.8 or 2.0 you have hydraulic valve lash adjusters. If your vehicle is beta2 you have mechanical lash adjusters.

Without the proper adjustment, or due to valve sticking, compression gases can leak back up into the air inlet manifold, increase the pressure, confuse the control computer that it's because the driver has opened the throttle wide and so it may choose to add more fuel. Surges are the result.

I remark "may" because most control computers are equipped with a throttle position sensor (to know where you really put the throttle), yet, believe it or with difficulty, some control boxes' softwares place more influence or emphasis on the inlet manifold pressure anyway, as if more important than where you place your foot.

On some vehicles with the MAP (manifold air pressure) sensor, it's possible to simply disconnect it, to get to a garage or safe place. On the Daewoo the MAP is right on top of the engine, just underneath the hood. The engine restarts in a more basic, less, um, nervous mode called TP. Hyundai may be similar or identical.

Garage techs do know of problems with valves on your model and even shim them . . . . . . nothing new? It's like the sixties!


Here is a link that might be useful: valve adjustment still matters

    Bookmark   November 18, 2014 at 6:00AM
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