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Thread: Bad TPS symptoms

  1. #1

    Bad TPS symptoms

    The following symptoms have presented themselves:

    1) One day I had an engine stumble at a pretty specified point in the throttle (seemed throttle position or load-related as opposed to RPM or speed). I could hold the throttle at that position and the engine would stumble and not accelerate, but any more or any less throttle and it was smooth. This problem was consistent for one drive cycle and has not presented itself since, but the other issues below remain.
    2) Engine not entering deceleration cutoff mode (DCO). When you lift off the throttle under load the fuel injection should shut off, air fuel ratio should go to infinite (I have a wideband O2 meter) and vehicle should decelerate. This isn't happening, I lift off the throttle, vehicle coasts like an automatic (it's a manual) and wideband stays at 14.7:1 AFR.
    3) Occasional inconsistent idle. Sometimes it decides it wants to idle high, particularly when cold. It used be consistent.
    4) No CEL has been presented.

    Otherwise, vehicle runs like a dream and goes like a raped ape. I'm thinking all signs point to TPS, particularly when I read this about fuel cutoff mode:
    Deceleration enleanment or fuel cut-off mode – is reached during periods of deceleration. In this mode, the ECM simply reduces injector pulse width or momentarily shuts the injectors off in order to reduce high emissions and engine backfire. The main signal inputs to the ECM for this mode are the TPS, RPM and the VSS (vehicle speed sensor). This is the reason why a faulty TPS signal that shorts to ground intermittently can send the system into fuel cutoff mode, creating a drivability concern. And, during this condition the ECM reacts as a closed throttle deceleration condition. Another common fault relating to this mode is in systems with an idle switch, whereby, the idle air bypass screw is set too high and the engine idles up-and-down between 900 and 1500 RPM. The reason for this is simply that the ECM is receiving a closed throttle signal (from the idle switch) and the idle speed is raising above normal, causing the ECM to cut injector pulse (injector cut-off mode). To solve this problem, adjust the idle air bypass screw, unless there is large vacuum leak, in which case repairing the vacuum leak will solve the problem. Once the TPS or idle switch signals the ECM of a closed throttle or idle condition and the RPM has dropped bellow a preset value, the system goes into idle-mode. There are other possible reasons why an ECM would activate the fuel cut off mode. For example – If the engine were to reach a pre-programmed high engine speed (high RPM), the ECM would cut injector pulse to protect the engine from damage. Also, if the vehicle reaches a pre-determined high speed, for safety reasons, some systems would momentarily cut fuel and ignition to protect the driver from damage.

    A new TPS is $52, so I'm thinking I will start there. Boost gauge shows 20 in vacuum at idle, so there is no vacuum leak. Could also be idle air controller according to the above, but I'm thinking my symptoms align with TPS, yes?

  2. #2
    Quote Originally Posted by paddlenbike View Post
    The following symptoms have presented themselves:


    Could also be idle air controller according to the above, but I'm thinking my symptoms align with TPS, yes?
    When my IAC was acting up I had more symptoms than you're reporting. I had starting issues, very low idle (~450 RPM) and stuttering that did not disappear once they showed up. It sounds like the TPS is a good place to start.

  3. #3
    TPS seems more likely. But both are problem children.
    2005 Lexus LX470 - Stock for now...

    1998 Toyota 4Runner SR5 V6 4x4 + a bunch of goodies. Lifted, Locked, Illuminated and Armored. Winner,"Best Offroad Truck" - 2010 Pismo Jamboree. It's been upside down and still drives me to work.

  4. #4
    Quote Originally Posted by Seanz0rz View Post
    TPS seems more likely. But both are problem children.
    TPS on order; I will report back.

    Also ordered a driver's side door check as the door will no longer stay open on my slanted driveway. They look pretty easy to replace. I found some complaints on the 5th gen 4Runner where the steel is so thin at the door check that it often flexes and breaks, meaning the door has to removed and beefed up from the inside. This is apparently a problem on Siennas too, so at least I don't have to deal with that.

  5. #5
    I would lean towards the TPS by the description of your symptoms.
    IAC is ofcourse a close second. I will be doing that myself with the inconsistent cold start idle I have been having.

    Quote Originally Posted by paddlenbike View Post
    TPS on order; I will report back.

    Also ordered a driver's side door check as the door will no longer stay open on my slanted driveway. They look pretty easy to replace. I found some complaints on the 5th gen 4Runner where the steel is so thin at the door check that it often flexes and breaks, meaning the door has to removed and beefed up from the inside. This is apparently a problem on Siennas too, so at least I don't have to deal with that.
    I recall a TSB back at Toyota for the weak metal for the door check on the Siennas, that unfortunate for the 5th gen.
    Last edited by YotaFun; 03-04-2017 at 10:23 AM.

  6. #6
    Replaced the TPS this weekend but not without one of the screws stripping. I had already removed the throttle body to gain access to the screws so as not to strip them out, but it ended up happening anyway. 30 seconds with a dremel and I had a new notch and got the screws out, now replaced with stainless steel allenhead bolts. Truck passed smog just fine.

    The hesitation issue only presented itself that one time, but for the past few weeks it has not consistently gone into deceleration cutoff when letting off the throttle, which meant it coasted like an automatic when lifting off the throttle. It's back to normal now.

    Not a very interesting post but perhaps it will help someone who is experiencing similar vehicle symptoms. This never did produce a CEL.

  7. #7
    Awesome news. Glad that it was an easy fix and you were able to track it down.

    Wonder how tolerant certain systems are the 3rd generation 4Runners.
    I've had a cold start idle issue in my 97 since last winter and its only in winter time...
    I also had a slow responding o2 sensor last summer, I cleared the code once it went on a few months without turning back on, I still changed the o2 anyway.
    I also had a injector going bad that would cause a back fire under heavy load but no CEL for that either, I swapped injectors with my donor motor and things have been fine since too.

  8. #8
    I am thankful that Toyota sensors are relatively inexpensive, the OEM Toyota TPS was only $51.

    The lease on my Nissan Leaf ended in January and the 4Runner is now my daily driver for my 37-mile commute. I miss not having to go to the gas station, it is fun getting to drive the 4Runner everyday.

  9. #9
    Glad you got that fixed.

    I'm commuting 50 rough day trip in the LX. 15mpg is hurting a little bit. Gotta get the 4runner back on the road soon! Just a steering rack, timing belt, and rear axle RR before I can do that.
    2005 Lexus LX470 - Stock for now...

    1998 Toyota 4Runner SR5 V6 4x4 + a bunch of goodies. Lifted, Locked, Illuminated and Armored. Winner,"Best Offroad Truck" - 2010 Pismo Jamboree. It's been upside down and still drives me to work.

  10. #10
    Quote Originally Posted by Seanz0rz View Post
    Glad you got that fixed.

    I'm commuting 50 rough day trip in the LX. 15mpg is hurting a little bit. Gotta get the 4runner back on the road soon! Just a steering rack, timing belt, and rear axle RR before I can do that.
    Luckily gas is still reasonable right now. As nice as the Leaf was to drive it was definitely a bit emasculating, whereas I get the thumbs up in the 4Runner. There is also a big difference in the way I get treated on the road, I don't get cutoff nearly as often in the 4Runner.

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