throttle stuck at/near wide open on hwy

[d_benet]

Yes, it was as scary as it sounds but I was able to avoid disaster. Mines a Sport 5spd so I was able to push in the clutch, shift to neutral...engine screaming...pull over to the shoulder and kill the motor.

This was the 3rd time this occurred. The first time was 2 years ago under similar circumstances; engine under heavy load going uphill at highway speed after an hour+ at hwy speed. Under the hood investigation revealed nothing unusual. Throttle linkage all looked normal and snapped back into position when depressed. Cable attachment looked good with no excess slack (although needing adjustment). I began poking and tapping around. I was able to temporarily solve the problem by tapping on the throttle body just above the butterfly valve causing the valve to shut. After repeated cycling/testing the throttle, I was able to limp home cautiously. Once home, I thoroughly cleaned the TB, MAF sensor, IAC and adjusted the throttle cable. I'm now at max adjustment and cable should probably be replaced due to stretching out. This all worked fine and the truck ran great for 1.5 yrs including a big Baja trip until it happened again last January. Under similar circumstances, and problem was again solved by tapping on TB. Again I very thoroughly (full removal and lots of pipe cleaners, Q-tips, and TB cleaner) cleaned the TB, IAC, MAF sensor and this time replaced the throttle position sensor. Now it has occurred again having only driven 2000 miles since the last incident so clearly something else is going wrong...and no...its not the floor mat.

I haven't been able to find any reports of TBs stuck open, but several reports of them sticking in idle. I haven't pulled it off to look closely yet, but my theory is the butterfly valve pivot shaft has worn where it seats in the wall of the TB. This is causing the valve to open off axis and catch on the inside of the TB when its at its widest opening ie at or near wide open throttle. Once there, friction overpowers the throttle return spring and it sticks there. I think this is worsened by the fact this vehicle only drives a 3-4K/year and almost none of that in the conditions that seems to cause this issue...ie I think the butterfly valve pivots fine within the normal range of daily around town throttle (I like to baby my truck), but catches when engine is hot and throttle is opened up to full.

1) Has anyone experienced or heard of this happening? 2) Does my theory sound reasonable? 3) There are separate part numbers for auto trans vs. 5 spd and I cannot find a used replacement for my 5spd. Can I use a TB off a 5VZ-FE auto (minus the kickdown cable of course)? I would like to avoid spending $550 on a new one.

EVERYONE PLEASE BE CAREFUL IF YOU EXPERIENCE THIS ISSUE

 

[gamefreakgc]

Yes, it was as scary as it sounds but I was able to avoid disaster. Mines a Sport 5spd so I was able to push in the clutch, shift to neutral...engine screaming...pull over to the shoulder and kill the motor.

This was the 3rd time this occurred. The first time was 2 years ago under similar circumstances; engine under heavy load going uphill at highway speed after an hour+ at hwy speed. Under the hood investigation revealed nothing unusual. Throttle linkage all looked normal and snapped back into position when depressed. Cable attachment looked good with no excess slack (although needing adjustment). I began poking and tapping around. I was able to temporarily solve the problem by tapping on the throttle body just above the butterfly valve causing the valve to shut. After repeated cycling/testing the throttle, I was able to limp home cautiously. Once home, I thoroughly cleaned the TB, MAF sensor, IAC and adjusted the throttle cable. I'm now at max adjustment and cable should probably be replaced due to stretching out. This all worked fine and the truck ran great for 1.5 yrs including a big Baja trip until it happened again last January. Under similar circumstances, and problem was again solved by tapping on TB. Again I very thoroughly (full removal and lots of pipe cleaners, Q-tips, and TB cleaner) cleaned the TB, IAC, MAF sensor and this time replaced the throttle position sensor. Now it has occurred again having only driven 2000 miles since the last incident so clearly something else is going wrong...and no...its not the floor mat.

I haven't been able to find any reports of TBs stuck open, but several reports of them sticking in idle. I haven't pulled it off to look closely yet, but my theory is the butterfly valve pivot shaft has worn where it seats in the wall of the TB. This is causing the valve to open off axis and catch on the inside of the TB when its at its widest opening ie at or near wide open throttle. Once there, friction overpowers the throttle return spring and it sticks there. I think this is worsened by the fact this vehicle only drives a 3-4K/year and almost none of that in the conditions that seems to cause this issue...ie I think the butterfly valve pivots fine within the normal range of daily around town throttle (I like to baby my truck), but catches when engine is hot and throttle is opened up to full.

1) Has anyone experienced or heard of this happening? 2) Does my theory sound reasonable? 3) There are separate part numbers for auto trans vs. 5 spd and I cannot find a used replacement for my 5spd. Can I use a TB off a 5VZ-FE auto (minus the kickdown cable of course)? I would like to avoid spending $550 on a new one.

EVERYONE PLEASE BE CAREFUL IF YOU EXPERIENCE THIS ISSUE

Get a new throttle body ASAP! The valve is sticking open for whatever reason, or the spring is completely worn out. Unfortunately you will need one from a manual, since you need a dashpot attached to it and autos don't have that. In the meantime, put a few drops of oil in where the butterfly valve rotates in the throttle body, that will keep it lubricated for a little bit.

Glad you have a manual or that would have been a life or death situation.

 

[4Reak Show]

Not sure manual TB is necessary. I have an auto 4Runner engine, and a manual Taco ECU/wiring. Runs fine for 8 years now.

I'll check under the hood for a dashpot on the TB but I'm pretty sure I don't have it.

Only thing ive seen it help with is keeping the throttle open a little during shifting. Just means you gotta shift faster!

 

[pluton]

I have no experience with the problem you describe, but my notion is the same as gamefreak: get a new one(check Amayama if you haven't). I had a mysterious high idle when I acquired my '97 in 2013. New TB, and now I have a lifetime(the truck's, not mine) of no problems ahead of me. $550 is cheap to fix it 'forever'.

 

[Mchaz]

Glad you have a manual or that would have been a life or death situation.

Why do you say that? An auto can be bumped into neutral from drive while under power. Your reaction on a clutch pedal may be a bit faster, but either an auto or manual trans can be put into neutral quite fast. Either way it would be scary!

OP, it sounds like you have found the smoking gun to be the throttle body. I would swap it out post haste. It's not worth your safety to keep trying to repair this one from the sound of it.

Sent from my RS988 using Tapatalk

 

[AntleredRuin]

I'd poke around at a junkyard first. Take several pictures of your current one, and compare to one before you buy it. Make sure they have a return policy, just in case. Hell, the TB is easy enough to change out, just do it in the parking lot, just in case.
TB issues are pretty rare, and this issue is virtually unheard of, so I wouldn't sweat at all putting a used TB in, as long as it seems clean and tight.
I have no problem with used parts to save money as long as they aren't known to break very often.

I got a used Fuel Pressure Regulator off eBay for $30 that's lasted me 50k and counting. A new one would have cost over $200.

And yeah, an auto can be put in neutral under load, no problem.

 

[gamefreakgc]

Why do you say that? An auto can be bumped into neutral from drive while under power. Your reaction on a clutch pedal may be a bit faster, but either an auto or manual trans can be put into neutral quite fast. Either way it would be scary!

OP, it sounds like you have found the smoking gun to be the throttle body. I would swap it out post haste. It's not worth your safety to keep trying to repair this one from the sound of it.

Sent from my RS988 using Tapatalk

Not everyone knows to do that in a situation like that though. Most incidents you see related to stuck pedal/throttle body it ends in a terrible crash since most vehicles are autos and people panic, even though they all have a neutral shift option. Manuals are much, much simpler since it's the gut reaction to take it out of gear.

 

[AntleredRuin]

Not everyone knows to do that in a situation like that though. Most incidents you see related to stuck pedal/throttle body it ends in a terrible crash since most vehicles are autos and people panic, even though they all have a neutral shift option. Manuals are much, much simpler since it's the gut reaction to take it out of gear.

I would think gut reaction would be to brake first.

To be fair with this statement, though, most people who drive manuals are more 'car people' than those who drive an auto. They are more aware of their vehicle and its workings and that alone will have them know what to do in a crisis of that nature.
I'd bet that most anyone on this forum would make it out of a situation like that safely, because we're all 'car people'. Transmission type aside.

Now take an average person who just happened to learn how to drive using a manual, and I doubt there would be much difference in outcome compared to an average person who learned how to drive using an auto.

 

[JohnMc]

+1 on the 'get another throttle body' bandwagon. You've had it apart a couple of times, seen nothing wrong, and it's done it again. Toss that haunted TB in the trash and get another one from a junkyard ASAP.

The part about the throttle sticking down that makes it so dangerous is that with the throttle on the floor, the engine certainly isn't making any vacuum. The brake booster has enough vacuum in it for only 2-ish power-assisted braking attempts. And most people just sort of tentatively dab at the brakes once or twice, before committing to haul the car down to a stop on the shoulder. And if you've given it a couple of taps already, and 'used up' the vacuum, it's incredibly hard to get the brakes to do much of anything without power assistance. You have to REALLY mash the pedal.

Obviously, slipping it into neutral in either a manual or an automatic car is the proper thing to do - let it bounce of the rev limiter while you stop and then turn it off. But people panic.

 

[alumarine]

Why not hit brakes and turn motor off?
You can still steer and brake with motor off.

 

[JayRolla]

Not everyone knows to do that in a situation like that though. Most incidents you see related to stuck pedal/throttle body it ends in a terrible crash since most vehicles are autos and people panic, even though they all have a neutral shift option. Manuals are much, much simpler since it's the gut reaction to take it out of gear.

It's not hard to bump into N then turn off. I have had my floor mat do the same thing. Another reason everyone should know how to drive a manual just to understand how cars work.

It's not rocket science. I would believe people are smart enough especially folks on this forum. I hope!

 

[phattyduck]

Why not hit brakes and turn motor off?
You can still steer and brake with motor off.

Leave the motor on, shift into neutral, whether manual transmission or auto. The engine can sit at redline all it wants - the ECU won't let it over-rev...

-Charlie

 

[DaMonkey]

Why do you say that? An auto can be bumped into neutral from drive while under power. Your reaction on a clutch pedal may be a bit faster, but either an auto or manual trans can be put into neutral quite fast. Either way it would be scary!

OP, it sounds like you have found the smoking gun to be the throttle body. I would swap it out post haste. It's not worth your safety to keep trying to repair this one from the sound of it.

Sent from my RS988 using Tapatalk

If you put an auto into neutral and the motor starts screaming, it will will coast fine until you shut the motor off. I think. I'm not sure about these trucks, but I'd think pump in transmission is in front behind the TC and will stop turning when the engine kills. If it doesn't lock up I'm sure it would at least be real bad for trans.

 

[gamefreakgc]

It's not hard to bump into N then turn off. I have had my floor mat do the same thing. Another reason everyone should know how to drive a manual just to understand how cars work.

It's not rocket science. I would believe people are smart enough especially folks on this forum. I hope!

Highways here in CA are always jammed with traffic. The closest car is roughly 2 seconds ahead of you up in the road. If it floors, you have approximately 5 seconds to figure out how to stop the vehicle. That's why the GM and Toyota recalls were such a big issue, people were ramming the cars in front of them at 75+ MPH.

I don't even know if I could react that fast. Especially if mine ever floored... I'd be going 100 MPH+ in a matter of seconds!!!

 

[d_benet]

+1 on the 'get another throttle body' bandwagon. You've had it apart a couple of times, seen nothing wrong, and it's done it again. Toss that haunted TB in the trash and get another one from a junkyard ASAP.

The part about the throttle sticking down that makes it so dangerous is that with the throttle on the floor, the engine certainly isn't making any vacuum. The brake booster has enough vacuum in it for only 2-ish power-assisted braking attempts. And most people just sort of tentatively dab at the brakes once or twice, before committing to haul the car down to a stop on the shoulder. And if you've given it a couple of taps already, and 'used up' the vacuum, it's incredibly hard to get the brakes to do much of anything without power assistance. You have to REALLY mash the pedal.

Obviously, slipping it into neutral in either a manual or an automatic car is the proper thing to do - let it bounce of the rev limiter while you stop and then turn it off. But people panic.

Thanks JohnMc, excellent points about the vacuum / brake booster; I had not even considered that yet. Also, good to know about the ECU limiting revs. I'll be ordering my new TB today.

Why not hit brakes and turn motor off?
You can still steer and brake with motor off.

I did not want to turn motor off until I was on the shoulder. Not sure about you guys, but my steering wheel locks when the key switch is in the off position. I would have to carefully turn key to ACC to successfully maintain steerage in an already sketchy situation.

 

[JohnMc]

I did not want to turn motor off until I was on the shoulder. Not sure about you guys, but my steering wheel locks when the key switch is in the off position. I would have to carefully turn key to ACC to successfully maintain steerage in an already sketchy situation.

I just double checked (on my '99, FWIW) and the steering wheel only locks when the key is pulled all the way out' not when merely turned to 'off'.

When you pull the key all the way out, you hear a little 'click', and at that point, the steering wheel locks if turned enough. When you put the key in, you have to turn it from 'off' to 'ACC' to unlock it.

 

[curryT4R]

I just double checked (on my '99, FWIW) and the steering wheel only locks when the key is pulled all the way out' not when merely turned to 'off'.

When you pull the key all the way out, you hear a little 'click', and at that point, the steering wheel locks if turned enough. When you put the key in, you have to turn it from 'off' to 'ACC' to unlock it.

It's literally called a Steering Lock. It helps prevent theft. You have to have the correct key that sends a signal from the key to the key ignition coil to the steering lock to unlock it. If someone without the correct key tried it, it would just lock in place and it can't go anywhere.

 

[JohnMc]

If someone tries the wrong key while he's driving on the freeway with the throttle stuck open, I'd really want to see a video. Lol.

Just saying, turning the key to the off position will not lock the steering wheel. It's only able to lock when the key is pulled out.

You would lose power steering with the engine off vs it bouncing off the rev limiter. With the throttle stuck open, no difference on the power brakes though. You get a couple of braking attempts before the pedal goes stiff and doesn't do much.

You can test that last part out fairly easily, obviously drive safely, watch out for traffic, etc, etc. But going at highway speeds, maybe up a hill so you don't accelerate too much (lol 4Runner power to weight ratio) floor the pedal, keep it floored, and press and release the brake pedal several times in a row. Braking, braking, braking?, stiff pedal and practically no braking at all.

 

[JayRolla]

Highways here in CA are always jammed with traffic. The closest car is roughly 2 seconds ahead of you up in the road. If it floors, you have approximately 5 seconds to figure out how to stop the vehicle. That's why the GM and Toyota recalls were such a big issue, people were ramming the cars in front of them at 75+ MPH.

I don't even know if I could react that fast. Especially if mine ever floored... I'd be going 100 MPH+ in a matter of seconds!!!

Lol. Supercharged 4runner is still slow.

1 car length every 10 mph. If your tailgating you deserve to wreck. That's the point of not tailgating.

 

[I_bRAD]

Lol. Supercharged 4runner is still slow.

1 car length every 10 mph. If your tailgating you deserve to wreck. That's the point of not tailgating.

Agreed on following at a safe distance. Disagree on 1 car length/10mph. Assuming a car is approx 16' long, at 60mph that only gives you 1s space. I think 3, or 4 if you can keep it is much safer.

Standard these days seems to be <2s, which drives me nuts. I drive on rural 50mph roads on my commute and I'll often pull off for a second to let people pass.