YotaTech Forums - 01 4runner throttle issue

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01 4runner throttle issue

so I'm having a issue where I will be driving down the road at a constant speed and all of a sudden I lose throttle responce, the vehicle will not react for 3 seconds, I can depress the pedal all the way to the floor and nothing happens, I'm wondering if it has to do with the fly by wire system on my vehicle like the tps or something, and to top things off I have no check engine light, I did hook up a scan tool to it and noticed that with the throttle fully depressed the tps sensor is only showing the throttle being at 79%, dunno if its supposed to be like that or what, well any info would be helpful

Vehicles without throttle cables disturb me, though I do trust Toyota more than most other brands. It does sound like and issue with either the pedal position sensor or the throttle servo itself. I think Toyota refers to the pedal position sensor as the TPS, maybe someone else could verify. I would definitely get this resolved a quickly as possible.

I'm confused...does the vehicle stay at the constant speed you mentioned when this happens, or does the engine just die? Or does the gas pedal essentially become worthless for 3 seconds?

so what the vehicle will do is when driving at a constant speed, the vehicle will drop the rpms down to idle like it died but it didn't die, when you go to push on the accelerator you get no response, for a maximum of 3 secs.

OK gotcha. Basically like you put it in neutral and took your foot off the gas.

You should hook up the scan tool and note (safely) where the TP is when this happens. That will help you isolate it a bit. Another idea is to obtain the FSM and follow the TBW test procedure. My guess is that with a multimeter you could have this nailed down.

Good idea, but a multimeter will not help you with a newer TPS, if it is a TPS issue.

The problem is that when you test it, a multimeter will not pick up the slight problem between the circuits. The ECU is able to throw a code because it can catch a slightly off reading in the TPS arm as it moves up and down.

If it is the TPS, you should definitely have a check engine light code (PO120 Throttle Position Sensor, A Circuit)

And if your throttle is open fully, it should not read "79%". FYI your TPS sensor does not need adjustment, nor does the position need to be noted when you remove it.

Quote:

Originally Posted by PismoJoe (Post 51456189)

Good idea, but a multimeter will not help you with a newer TPS, if it is a TPS issue.

Are you sure?

I'll admit I don't have a lot of experience with TBW, but this article seems to advocate the use of a DVOM for diagnostic purposes.

Extract (my emphasis in bold):

Quote:

THROTTLE-BY-WIRE DIAGNOSTICS

Most of the faults that occur in a Throttle-By-Wire control systems are things you would expect, like pedal or throttle position sensors that wear out and skip or produce erratic signals, motor failures in the throttle body, and electrical problems like loose or corroded wiring connectors.

A code reader or scan tool is required for diagnostics. Generic OBD II trouble codes for possible pedal position sensor faults include P0120 through P0124, P0220 through P0229, plus any OEM enhanced P1 or P2 series codes for that specific vehicle.

If a fault occurs in the motor on the throttle body, it will be detected by the feedback signals from the throttle position sensors. Generic OBD II codes for this kind of problem include P0638 & P0639, plus any OEM enhanced P1 or P2 series codes for that specific vehicle.

The Throttle-By-Wire system also monitors the throttle position sensors on the throttle body. A fault here may set any of the same OBD II codes just listed for the pedal position sensor, or OEM enhanced P1 or P2 series codes for that specific vehicle.

Diagnosis involves reading the fault code(s) to determine the circuit that is experiencing the problem, then checking the voltage or resistance of the pedal or throttle position sensors with a DVOM, or checking the operation of the throttle control motor (visual observation of the throttle when the motor is commanded to move, and/or checking the duty cycle commanded by the control module using a scan tool).

When the fault has been identified, the faulty part can then be replaced. The codes can then be cleared, and hopefully everything will work correctly again.

I didn't mean that you can't test the TPS, I was saying that the problem usually is very difficult to pinpoint. I'm talking specifically if this is a TPS issue. (PO120, PO124 etc like you were saying)

The arm moves too fast for a multimeter to detect it any off reading, thats why this article seems to push the use of an OBDII scanner tool, in which the codes will point to the TPS, if there is the problem there.

I have done about 5 TPS sensors in the 95.5-04 year range, only one of them proved faulty by via the resistance test. It is possible, but like I was saying, most of the time you will not be able to detect the problem within the TPS.

Makes sense. Thanks!