What could cause unresponsive throttle?

[TJM]

Alright you gearheads, I'm stuck in the mud here and I need a hand figuring what in the nine hells is going on with my Runner.

Once in a while (usually several times per hour) I hit the gas from a dead stop and go nowhere.

RPMs don't rise, vehicle doesn't move, tires don't turn.

Here's the rundown of what I know:

1. It's not the throttle body. I cleaned that and it didn't help.
2. It has gotten worse over the last two months as far as frequency of occurrence.
3. Overall it will last from five to fifteen seconds per incident
4. It's really f'n annoying, and potentially dangerous
5. No engine light has come on.

I don't think it's the MAF, because no engine light.

All I can think of is fuel pump or throttle position sensor (going off what I've heard from others.

Other than that, I don't know where to begin. Any ideas? Similar issues? Words of wisdom?

 

[MN4runnerman]

I had the same issue on my 2002 and also on my 2001 and have yet to figure it out. I think it has something to do with fuel sending unit or something with it but could be dead wrong. For all I know it could be something with the computer not registering a throttle response too.

 

[TJM]

Well, so far it's beyond me, so I guess I will have to bite the bullet and pay to have it investigated. I've tried to find out through the forums before but noone seems to know or want to hazard a guess.

 

[stir_fry_boy]

Lots of things can cause engine hesitation like injectors, spark plugs, clogged air filter, insufficient fuel pressure, try sea foam in the gas tank with premium fuel first as well as pulling a spark plug to make sure they are Denso/NGK OEM.

 

[MN4runnerman]

It doesn't happen very often to me so its low on my priority list but if you find out post it cuz I really want to know so then I know what to fix

 

[kball]

Alright you gearheads, I'm stuck in the mud here and I need a hand figuring what in the nine hells is going on with my Runner.

Once in a while (usually several times per hour) I hit the gas from a dead stop and go nowhere.

RPMs don't rise, vehicle doesn't move, tires don't turn.

Here's the rundown of what I know:

1. It's not the throttle body. I cleaned that and it didn't help.
2. It has gotten worse over the last two months as far as frequency of occurrence.
3. Overall it will last from five to fifteen seconds per incident
4. It's really f'n annoying, and potentially dangerous
5. No engine light has come on.

I don't think it's the MAF, because no engine light.

All I can think of is fuel pump or throttle position sensor (going off what I've heard from others.

Other than that, I don't know where to begin. Any ideas? Similar issues? Words of wisdom?

Since you don't say what year you have I'll guess it's a 01-02. I can't imagine a bad TPS causing you to go no where when hitting the gas unless you are fly by wire. My guess is, a bad TPS, bad thing is, if you are an 01-02 I don't think you can get just the TPS. I think you have to get the whole TB.

 

[MTD]

3.4L



Jokes, I got em'. lol

 

[A.Wilson013]

No one has mentioned fuel filter, but I'd be willing to bet yours is 13 years old and could use a change even if just for maintenance...

If I were in your shoes my first step would be to buy a scanning tool that's capable of monitoring fuel trims, ignition timing, all that jazz. With that, when the problem is occuring you'll be able to see pretty quickly if it's fuel related, ignition related, or neither.

Testing the fuel pump is simple if you've got a multimeter. There's an access panel under the rear seats that will allow you to check the resistance without doing any real mechanic work.

I think the TPS is also a simple part to troubleshoot, but I've never done it, so I cannot speak too much on that.

A scan tool would also be able to tell you if when you're giving it gas, the throttle is not opening, or opening too little.

 

[TJM]

Lots of things can cause engine hesitation like injectors, spark plugs, clogged air filter, insufficient fuel pressure, try sea foam in the gas tank with premium fuel first as well as pulling a spark plug to make sure they are Denso/NGK OEM.

I tried Seafoam, and I've been putting premium in in since I got it. No dice so far. Haven't tried the spark plugs yet, but they'd all have to be bad at the same time to act like that. Still, it's on my list of replacement parts to get to.

 

[TheDurk]

Since you don't say what year you have I'll guess it's a 01-02. I can't imagine a bad TPS causing you to go no where when hitting the gas unless you are fly by wire. My guess is, a bad TPS, bad thing is, if you are an 01-02 I don't think you can get just the TPS. I think you have to get the whole TB.

Agree with this. There is also the pedal sensor which other years don't have and can be changed on its own. I recommend OP spend some time with the 1996 to 2002 Toyota 4Runner OEM Repair and Wiring Manuals FSM and test all the components of the Throttle-by-wire system. The intermittent nature of the fault makes me think it is electrical. I don't know enough about the TbW system to suggest what components can cause a problem without setting a code.

This is all assuming he is '01-'02 which would be really nice to know.

 

[TJM]

It's an 02

 

[TJM]

Okay so with the responses so far I'll be replacing the spark plugs and fuel filter, maybe even the throttle body or, if possible, only the throttle position sensor.

Does anyone think it can be the fuel pump itself? Or corroded fuel lines? Theres a lot of rust underneath and it looks like part of the lines could be compromised.

 

[TJM]

Agree with this. There is also the pedal sensor which other years don't have and can be changed on its own. I recommend OP spend some time with the 1996 to 2002 Toyota 4Runner OEM Repair and Wiring Manuals FSM and test all the components of the Throttle-by-wire system. The intermittent nature of the fault makes me think it is electrical. I don't know enough about the TbW system to suggest what components can cause a problem without setting a code.

This is all assuming he is '01-'02 which would be really nice to know.

Is that available in a PDF form or anything downloadable? I don't always have the best wifi connection in the shop, and I like to have this kind of thing pulled up.

 

[TheDurk]

Is that available in a PDF form or anything downloadable? I don't always have the best wifi connection in the shop, and I like to have this kind of thing pulled up.

It's out there, but I don't have a link. (I have a paper one for my year so I don't need it.) Hopefully, someone else can help you.

 

[SupaSupra]

My .02:

I was playing with the Traction Control fuse one day in my 01, if you unplug it the truck will barely move. Wouldn't hurt to check that out.

 

[JohnMc]

It's an 02

Electronic throttle then.

How does the engine run when it isn't responding to the pedal? Is it just idling normally? No change, or very little change at all? Or is it sputtering, bucking, coughing, wheezing, in some manner straining somewhat but not making any power?

Electronic throttle means that they took a $15 cable that runs from the gas pedal to the throttle and replaced it with a $$$ electronic throttle actuator. The pedal has no mechanical connection to the throttle, it's just a hooked to an electronic rheostat that measures how far you're pushing it down. And the the ECU figures out how far it wants to open the throttle based on that and other things (like traction control, as mentioned above, if ti thinks a wheel is spinning it's not going to open it as much), and then a signal is sent to the throttle body to have a little electric motor open the throttle.

Obviously, there are a number of things that can go wrong in that whole setup, it's not as dumbly reliable as a cable is. Could be the switch, could be the little motor in the throttle body, could be the ECU thinking it shouldn't open the throttle for some reason. Complicated systems require complicated troubleshooting.

 

[TheDurk]

Electronic throttle then.

How does the engine run when it isn't responding to the pedal? Is it just idling normally? No change, or very little change at all? Or is it sputtering, bucking, coughing, wheezing, in some manner straining somewhat but not making any power?

Electronic throttle means that they took a $15 cable that runs from the gas pedal to the throttle and replaced it with a $$$ electronic throttle actuator. The pedal has no mechanical connection to the throttle, it's just a hooked to an electronic rheostat that measures how far you're pushing it down. And the the ECU figures out how far it wants to open the throttle based on that and other things (like traction control, as mentioned above, if ti thinks a wheel is spinning it's not going to open it as much), and then a signal is sent to the throttle body to have a little electric motor open the throttle.

Obviously, there are a number of things that can go wrong in that whole setup, it's not as dumbly reliable as a cable is. Could be the switch, could be the little motor in the throttle body, could be the ECU thinking it shouldn't open the throttle for some reason. Complicated systems require complicated troubleshooting.

Just to be clear, there IS a mechanical cable from pedal to the TB, but it is just a back-up "limp-home" function. It will only partially open the butterfly, allowing limited RPM's from the motor if the TbW goes down.

 

[TJM]

Electronic throttle then.

How does the engine run when it isn't responding to the pedal? Is it just idling normally? No change, or very little change at all? Or is it sputtering, bucking, coughing, wheezing, in some manner straining somewhat but not making any power?

Electronic throttle means that they took a $15 cable that runs from the gas pedal to the throttle and replaced it with a $$$ electronic throttle actuator. The pedal has no mechanical connection to the throttle, it's just a hooked to an electronic rheostat that measures how far you're pushing it down. And the the ECU figures out how far it wants to open the throttle based on that and other things (like traction control, as mentioned above, if ti thinks a wheel is spinning it's not going to open it as much), and then a signal is sent to the throttle body to have a little electric motor open the throttle.

Obviously, there are a number of things that can go wrong in that whole setup, it's not as dumbly reliable as a cable is. Could be the switch, could be the little motor in the throttle body, could be the ECU thinking it shouldn't open the throttle for some reason. Complicated systems require complicated troubleshooting.

Everything's normal except the response to the throttle. RPMs are at normal idling level, all pistons firing smoothly, no strange noise, just no get up and go.

 

[TJM]

Lame bullshit

Take the spam elsewhere

 

[diverscale]

clogged fuel filter, clogged air filter, bad spark plugs/wires, low fuel pressure, all of this won't cause the only symptom you are describing.

You clearly have a problem related to the fly-by-wire throttle system. If the throttle plate WAS opening, and the vehicle would not get-up-and-go, you would get a LOT of jerkiness and maybe a stalled engine due to the bad mixture. You didn't mention any jerkiness when the problem occurs.

Instead of hitting everywhere blind, you could get a 150$ OBD2 scanner, that can read real-time data (or even better, a scangauge II), and plug it when you are driving, when the symptoms occurs, look at the ''throttle %'' signal and play with the gas peddle. If nothing happens on the scanner, then it's the throttle plate not opening, then you have your problem pinpointed. Just don't forget that this signal % value is also related to the TPS sensor in your diagnostic.

By your brief description, it is 90% sure that your throttle plate is not opening past idle.