Runaway Engine

[pkanalyst]

Today I backed my 2022 Bronco out of the driveway and drove down the road about 1/2 mile. As I started braking for the stop sign, I noticed it was hard to slow it down and impossible to come to a complete stop. I threw it into neutral and the engine raced to 4400 rpms, holding steady there. I shut it down, put it in park and restarted it. In park it raced again to 4400 rpms. I shut it down again for a minute and the next time I restarted, it behaved normally and I drove 3 miles to where I was headed without any issues. Anyone experience this? I’m obviously concerned this could happen again without warning and will also be hard for a dealer to diagnose if they can’t duplicate the condition. But I don’t trust it anymore.

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[illverado]

While that’s not normal I can see how it might be possible for that to happen if you always start it and immediately go without ever letting it idle in neutral to trim adaptive idle control down. I’ve heard of this on a leased vehicle before that got started and floored out of the driveway every day for months without ever idling. The ecu commands extra air so it starts up, and trims it down after a few seconds. If it starts trimming and every day it is bogged down below target idle rpm, it adds throttle at that exact instance to bring it up to the target rpm. and if before it reacts to that change you’re applying throttle so it’s no longer trying to hit the target idle rpm, it just added throttle and saved that change. Stack this effect over and over and it is possible. Otherwise something is just definitely wrong with it lol like battery almost dead, unmetered air intake, mechanical issues etc

 

[pkanalyst]

While that’s not normal I can see how it might be possible for that to happen if you always start it and immediately go without ever letting it idle in neutral to trim adaptive idle control down. I’ve heard of this on a leased vehicle before that got started and floored out of the driveway every day for months without ever idling. The ecu commands extra air so it starts up, and trims it down after a few seconds. If it starts trimming and every day it is bogged down below target idle rpm, it adds throttle at that exact instance to bring it up to the target rpm. and if before it reacts to that change you’re applying throttle so it’s no longer trying to hit the target idle rpm, it just added throttle and saved that change. Stack this effect over and over and it is possible. Otherwise something is just definitely wrong with it lol like battery almost dead, unmetered air intake, mechanical issues etc

Well I wouldn’t say I always start it and drive right away though I have sometimes. In this case it had been idling for about 10 minutes to warm it up because it’s below freezing and snowing. Then it was shut off for a few minutes before starting it up and driving it. I hope that it is not a faulty throttle that is sending inaccurate commands when the pedal isn’t depressed.

Your explanation might also explain why sometimes it hesitates to back up occasionally right after starting it though.

 

[orion]

Today I backed my 2022 Bronco out of the driveway and drove down the road about 1/2 mile. As I started braking for the stop sign, I noticed it was hard to slow it down and impossible to come to a complete stop. I threw it into neutral and the engine raced to 4400 rpms, holding steady there. I shut it down, put it in park and restarted it. In park it raced again to 4400 rpms. I shut it down again for a minute and the next time I restarted, it behaved normally and I drove 3 miles to where I was headed without any issues. Anyone experience this? I’m obviously concerned this could happen again without warning and will also be hard for a dealer to diagnose if they can’t duplicate the condition. But I don’t trust it anymore.

Could have been the gas pedals potentiometer stuck at a certain position??? Maybe if it happens again blip the throttle and see if that stops it.

 

[Bschurr]

Throttle position sensor & adaptive trim each sound plausible.

Extra throttle / high idle is typically associated with an intake leak. Any codes?

 

[pkanalyst]

No check engine or any other dash indicators. FordPass doesn’t indicate any issues. I’ll plug in the OBD and see if it says anything.

 

[Figmo]

Did you try stomping the gas pedal while it was running away in park? If it was a stuck throttle sensor that might have jarred it loose. Also you said it was a freezing day - perhaps that caused something to stick. And running the vehicle for a few minutes warmed things up enough.

 

[pkanalyst]

Did you try stomping the gas pedal while it was running away in park? If it was a stuck throttle sensor that might have jarred it loose. Also you said it was a freezing day - perhaps that caused something to stick. And running the vehicle for a few minutes warmed things up enough.

At the time I didn’t although I sensed it come back up as I switched to the brake. I checked it when I got home and there were no obstructions (ie floor mat) and it traveled smoothly with nothing binding it up at all. At the time, the only change seems to be that I shut it off and let it sit for a minute then restarted it, which seems to have rebooted something.

I’m not a fan of modern vehicles being so software focused. All software breaks in ways that programmers can’t anticipate until it happens.

 

[BadlandsA51]

Today I backed my 2022 Bronco out of the driveway and drove down the road about 1/2 mile. As I started braking for the stop sign, I noticed it was hard to slow it down and impossible to come to a complete stop. I threw it into neutral and the engine raced to 4400 rpms, holding steady there. I shut it down, put it in park and restarted it. In park it raced again to 4400 rpms. I shut it down again for a minute and the next time I restarted, it behaved normally and I drove 3 miles to where I was headed without any issues. Anyone experience this? I’m obviously concerned this could happen again without warning and will also be hard for a dealer to diagnose if they can’t duplicate the condition. But I don’t trust it anymore.

Did you get a Wrench Light? What kind of floor mats do you have? Unintended acceleration just doesn’t happen since electronic throttle control, there are too many fail safes on Fords. Toyota had the problem several years ago, but at the time their system lacked any fail safes.

 

[Fly by Nite]

.... What kind of floor mats do you have? ......

x2 Check your floor mat!

 

[pkanalyst]

Did you get a Wrench Light? What kind of floor mats do you have? Unintended acceleration just doesn’t happen since electronic throttle control, there are too many fail safes on Fords. Toyota had the problem several years ago, but at the time their system lacked any fail safes.

No wrench light and OBD II showed no codes. Floor mats are locked in place and nowhere near the throttle so I’m not concerned there.

I’ve been unable to duplicate it today, but flooring it in park showed the revs are limited at 4,400 well before the pedal reaching the floor, indicating what I saw yesterday was either an effect of the throttle being at least halfway pressed (I firmly don’t believe this is the case), something interfering with the throttle position sensor (whatever that is seems to have cleared), or software gremlins. But if that were the case, I don’t think I’d be the first one to post about such a thing on here with this vehicle being in its 4th model year. I’m baffled.

 

[BadlandsA51]

I don’t know. There are 2 throttle position sensors that read opposite of each other and 2 accelerator pedal sensors that read opposite of each other. The PCM constantly monitors them and does plausibility calculations to make sure they all are working correctly. If there is any discrepancies, it turns the wrench light on and limits power to avoid a runaway. I have never heard of a failure of that system on a Ford. I’ve been around Ford service since way before electronic throttle control.

 

[BadlandsA51]

No wrench light and OBD II showed no codes. Floor mats are locked in place and nowhere near the throttle so I’m not concerned there.

I’ve been unable to duplicate it today, but flooring it in park showed the revs are limited at 4,400 well before the pedal reaching the floor, indicating what I saw yesterday was either an effect of the throttle being at least halfway pressed (I firmly don’t believe this is the case), something interfering with the throttle position sensor (whatever that is seems to have cleared), or software gremlins. But if that were the case, I don’t think I’d be the first one to post about such a thing on here with this vehicle being in its 4th model year. I’m baffled.

Any aftermarket tune or throttle enhancer module installed?

 

[the poacher]

As an aside, letting your Bronco idle for 10 minutes waiting for it to warm up is not good for your Bronco, or the environment, or any ICE vehicle for that matter.

Should You Warm Up Your Car? - Why Warming Up Your Car Is Bad (roadandtrack.com)

 

[pkanalyst]

As an aside, letting your Bronco idle for 10 minutes waiting for it to warm up is not good for your Bronco, or the environment, or any ICE vehicle for that matter.

Should You Warm Up Your Car? - Why Warming Up Your Car Is Bad (roadandtrack.com)

It truly was an exception. I appreciate what you’re saying and I don’t typically do that. I’m building a new house and was meeting with my PM at the site. The house is framed up but still open to the elements. My wife was running late and while we were waiting, the temperature dropped and it began to snow so we sat in the Bronco and ran it to get warmed up ourselves. When my wife arrived, I shut it off, we did our walk around and about 15 minutes later we left. I backed out of the driveway which is about 250’ long at idle speed with no issues. I backed out onto the road, turned, shifted to drive and went forward with no issue. The problem didn’t show up I tried to come to a stop 1/2 mile down the road.

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