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Discussion Starter · #1 ·
My brother just bought a used 2005 Mercury Sable (I think the Vulcan engine, but I haven't seen the car yet). On his way to work, he started to brake, and the RPM's shot up to 4000RPM like it was trying to accelerate on him.

What can cause this? I don't know how often it happens.
 

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My brother just bought a used 2005 Mercury Sable (I think the Vulcan engine, but I haven't seen the car yet). On his way to work, he started to brake, and the RPM's shot up to 4000RPM like it was trying to accelerate on him.

What can cause this? I don't know how often it happens.
Accidentally hitting the accelerator pedal while applying the brake? :dunno:
 

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Really bad downshift? When my speed sensor went out, occasionally I would be at speed and the car would drop into 2nd or third gear.
 

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Check the accelerator and cruise control cables, make sure they're moving freely and not binding, as well as the throttle body (it could be dirty). How is the car running otherwise? Could there be any kind of vac leak (in perticular from around the intake air control valve housing)? Check with starting fluid when the engine is cool and at idle, have a rag handy to wipe off excess.
 

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Discussion Starter · #6 ·
Check the accelerator and cruise control cables, make sure they're moving freely and not binding, as well as the throttle body (it could be dirty). How is the car running otherwise? Could there be any kind of vac leak (in perticular from around the intake air control valve housing)? Check with starting fluid when the engine is cool and at idle, have a rag handy to wipe off excess.
I haven't even seen the car yet. He's bringing it over tomorrow, and I'm going to check all that stuff out for him. I mean the throttle sticking has to be the only thing that could cause the car to do this, other than some sort of crazy cruise control malfunction ( he wasn't using it at the time though so it would have to be an insane malfunction).

He almost hit the car in front of him. But after that one time, it hasn't done it to him again. Maybe the car sat for a long time and got all sticky or something?

He still has his 30 day warranty, so he's going to take it back. But I doubt they'll do anything but clean the throttle body for him.

Hopefully that's all it is. If I find anything new out I'll post
 

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If you can not repeat this problem consistently I would say its an operator error.

From my experience I have done this same scenario a couple of times on my '97 Mercury Sable. Here's what happens. take a good look at your shoes and or boots. Look to see how WIDE they are. If the width of your shoes can overlap the brake pedal and accelerator pedal that is probably the root cause of the problem.

Here's what happens during real-time when driving, while pressing on the brake pedal the width of your shoe may not covering all the pedal and simultaneously pressing the accelerator pedal. This causes the car to brake and rev abnormally high at the same time, probably not good for the transmission either.

The 1st time I did this it really freaked me out because I thought there was some thing wrong with the car.

Solution make a conscious effort to put more of your foot on the brake pedal. I do not agree or like the idea of these two pedals being close to each other (bad design IMHO) but the fix is simple.

Let me know what you think.

Monsoon
 

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99% of reported unintended acceleration cases (excluding the Toyota ETC mess) were traced to the driver hitting the gas instead of the brake, often in a car that they were not familiar with. Unless you are packing 500 HP under the hood, the braking system will hold the car back even if going to WOT.
 

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Discussion Starter · #10 ·
Ok today it happened again, but not as bad. The weird thing is, it happened at the exact same spot on the road. It was a slight downhill. It's fine on other hills though.

That kind of has me worried. Could it be some weird transmission thing? If so I doubt that could cause acceleration (he was fighting the gas and had to shift to Neutral before he hit a car).

Maybe it was just coincidence, I don't know. He still hasn't come by for me to look at. He says the throttle feels free (not catching). But I need to see for myself.

Any more ideas would be welcome!
 

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Ok today it happened again, but not as bad. The weird thing is, it happened at the exact same spot on the road. It was a slight downhill. It's fine on other hills though.

That kind of has me worried. Could it be some weird transmission thing? If so I doubt that could cause acceleration (he was fighting the gas and had to shift to Neutral before he hit a car).

Maybe it was just coincidence, I don't know. He still hasn't come by for me to look at. He says the throttle feels free (not catching). But I need to see for myself.

Any more ideas would be welcome!
How long has he owned the car? Does your state have a "cooling off period"? Take it back to the dealer, and tell them what is going on. Hopefully they can replicate the problem. Maybe the VSS is going bad? Maybe you should try driving the car in the exact spot and see if you can replicate? Just be careful!
 

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As I said, check the Vehicle Speed Sensor (VSS). The most alarming thing about downshifts on a downhill grade is the amount of engine braking that it induces. Pretty unsettling when everything else is working fine.
 

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I'm itching to think IAC faulty. When you decelerate it automatically takes over for idling the vehicle vs the throttle plate when under throttle. When you come off the throttle, it can stick causing the vehicle accelerate similar to a vacuum leak, and then unstick when the throttle is applied again.

But it could be a VSS issue.
 

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I like the sticking IAC idea, as there was a replacement TSB out for a sticking IAC, on a bunch of 95 & 96 Ford vehicles & the 95 Taurus & Sable were on the list.

My 99 Ranger from time to time suffered from the same high rpm problem when coming to a stop & a new IAC fixed it.

Cleaning the IAC often doesn't last long & it didn't for me on the Ranger, but was a good trouble shooting step for me. I suppose thats why Ford recommends replacement, rather than cleaning!!!

So if he bought it from a Dealer, run that puppy by while it's still in warranty & have them refer to TSB 97-9-5, maybe he'll get a new IAC at no cost.

More thoughts for consideration, let us know what you find.
 

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Ok today it happened again, but not as bad. The weird thing is, it happened at the exact same spot on the road. It was a slight downhill. It's fine on other hills though.

That kind of has me worried. Could it be some weird transmission thing? If so I doubt that could cause acceleration (he was fighting the gas and had to shift to Neutral before he hit a car).

Maybe it was just coincidence, I don't know. He still hasn't come by for me to look at. He says the throttle feels free (not catching). But I need to see for myself.

Any more ideas would be welcome!
I had a similar problem, after attempting to swap the 60mm throttle body onto my vulcan I got bad readings from the throttle position sensor and my engine revved to 4000 in neutral (1800 in drive I couldnt get the thing to stop), I did throw a code for bad readings though.
 

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Discussion Starter · #16 ·
Ok, so I finally got a look at it. Hooked up my OBD II program and watched the TPS data as I pushed the throttle to the floor a bunch of times. When off, it kept going back to 17.5. But once it got stuck at 25. I quick tap on the pedal put it back to the normal 17.5

I looked under the hood and the cruise control throttle cable was off. I tried clipping it back on, but it kept popping off.

Here's my theory, I think the cruise cable has been off, and once in a while, gets lodged just right, not allowing the throttle to return fully to resting position.

I also found an OBDII code P0A11, DC/DC converter open, whatever the heck that means. I'll post another thread about that though.
 

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My brother just bought a used 2005 Mercury Sable (I think the Vulcan engine, but I haven't seen the car yet). On his way to work, he started to brake, and the RPM's shot up to 4000RPM like it was trying to accelerate on him.

What can cause this? I don't know how often it happens.

sorry did not read the hole post yet not sure if it got fixed. any way i just odered fuel injectors from rock auto for the same problem. it is a pontiac fiero with a red hot exhaust manifold and reveing at 4 k rpm. i thought it was a pluged cat or a fuel isssue because of the red hot header removed the cat and ended out being no fire brick in it. glad there was no brick now that narrows it down to fuel injectors. there is a way to test the fuel system wile running you need a fuel pressure tester. the normal presure should be like 40 psi with engine running it should drop 5-10 psi. not sure of these presure so read your manual on how to do it etc...
 

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I had the same issue not long ago. I threw an iac at it because when I popped the hood and tapped on it the rpms went down. Same problem after the new iac then I noticed the throttle was stuck and popped back when I wacked it. The cruise cable was off. You are correct, every once in a while the cruise cable catches and keeps the rpms up. I used electrical tape to keep the cable retracted and haven't had the revving issue since. I don't use cruise anyway, better gas mileage with the foot.
 

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Ok, so I finally got a look at it. Hooked up my OBD II program and watched the TPS data as I pushed the throttle to the floor a bunch of times. When off, it kept going back to 17.5. But once it got stuck at 25. I quick tap on the pedal put it back to the normal 17.5

I looked under the hood and the cruise control throttle cable was off. I tried clipping it back on, but it kept popping off.

Here's my theory, I think the cruise cable has been off, and once in a while, gets lodged just right, not allowing the throttle to return fully to resting position.

I also found an OBDII code P0A11, DC/DC converter open, whatever the heck that means. I'll post another thread about that though.
Hello there,

Can you please tell me if this issue was indeed the cruise control cable, and whether it was resolved after fixing it. My wife's car is doing the same thing and I am fearing for her safety, thanks.
 

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Just happened upon this post while checking for TPS info. I had the exact same thing happen to me. One of the little plastic clips that holds the cruise cable to the throttle had broken and it was causing the cruise cable to get stuck sometimes, which was holding open the throttle. Man, talk about a weird and scary feeling. I'm sitting there coasting and the car is actually accelerating. Sheesh. Seriously thought I was gonna die. So, I just fixed mine with superglue, and it has been good to go ever since.
 
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