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I have a 2000 Tundra 4.7 with 175K on it was it running great! Driving in traffic the other day and i realize that i have no gas peddle response...D'OH! I know, sounds familiar from other threads but bear with me. All gauges read normal, trans is in "D" and zero throttle response! Put'er in neutral and push the gas and get nothing. Push harder and WAM...POWER! Later, i read out the code (P0120?) which says "...error throttle position sensor...". I've replaced the TPS and no change. Removed positive batter cable to reset ECM but no change. I did notice that in actuating the throttle cable assembly side that the throttle body does not open until just about at the end of its travel and the throttle body "butterfly" is not 100% at the end of its travel (actual throttle position just like the gas peddle). More interestingly is that i cannot make the butterfly open 100% from the passenger side (throttle cable side). I can make the butterfly open 100% from the TPS or drivers side. Weird that i get different ranges of butterfly motion from opposite sides.

Opinions, please? Do i have a bad APPS or Throttle Control Motor (TCM)? Or...?
 

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Do i have a bad APPS or Throttle Control Motor (TCM)? Or...?
You have a bad APPS (Accelerator Pedal Position Sensor).

Been there, had that, on an '00 Tundra and '01 Sequoia, both with the 4.7L engine.

It is mounted on the passenger side of the throttle body. Replacing it is easy.

Unplug the connector.

Rotate the pully the throttle cable is wrapped around to the full throttle position and unhook the cable from it.

Remove the three screws that hold it on.

Pull it off.​
To install the new one, just reverse these steps. You will have to rotate it counterclockwise a bit to slide it in place, then rotate it clockwise to line up the screw holes.

No recalibration is required.

I did notice that in actuating the throttle cable assembly side that the throttle body does not open until just about at the end of its travel and the throttle body "butterfly" is not 100% at the end of its travel (actual throttle position just like the gas peddle). More interestingly is that i cannot make the butterfly open 100% from the passenger side (throttle cable side). I can make the butterfly open 100% from the TPS or drivers side. Weird that i get different ranges of butterfly motion from opposite sides.
It's not weird once you understand how the throttle control works. Refer to the attached .pdf file.

This throttle control system is called a "Drive By Wire" system. The idea is that the gas pedal does not directly control the throttle butterfly, rather the ECU does.

The gas pedal moves a cable, which moves the APPS sensor, which tells the ECU what throttle butterfly position the driver desires. In response, the ECU drives a servomotor (the TCM, or Throttle Control Motor), on the driver side of the throttle body, to open the throttle butterfly to the desired position. Next to the TCM is the TPS (Throttle Position Sensor), which senses the position of the throttle butterfly and provides feedback to the ECU so that it can control the throttle butterfly position precisely. This is an ordinary "closed loop" servomotor control system.

Your APPS is worn, such that it does not properly sense the accelerator pedal position. It is a rotary potentiometer, i.e. a long resistor with a rubbing contact that is mounted to the shaft. Rotating the shaft thus varies the resistance. The rubbing contact is badly worn in places, such that rotating the shaft from "idle" to "full throttle" does not properly result in a measure of its position. In my case (both time), it was a bit "numb" when coming off idle. Yours is more like "dead" until suddenly it makes contact that means "zoom!"

The cable and the mechanism under the APPS serves a "backup" function. In the event the APPS / ECU / TCM / TPS system won't work properly, you can press the throttle down a long way and it will open the throttle butterfly "manually". It won't open it very far, but you can "limp home" with it until you can get it serviced. This mechanism does not come into play at all when the system works normally.

If you need to use the backup system until you get a replacement sensor, just unplug the APPS and drive it, and the worn out APPS won't surprise you.
 

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Discussion Starter #3
DJ, thank you so much for your explanation! It is nice to know that the replacement procedure is relatively simple. It is not nice to know that the replacement part is ~ $300 and not widely available from my usual sources (e.g. Amazon, etc.).
 

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< Update >

Well, the new APPS arrived and got it installed as you said. "That was easy"! Naturally, i immediately fired 'er up. It stalled a few times but came to life. Now it idles well but peddle feeling still isn't quite back to normal. I disconnected the battery (read that somewhere that needs to be done) and seems about the same. I also read that the ECM will need to re-learn. Keeping in mind that my other variable is that i also replaced the TPS, does this sound about right to you?
 

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Just give it a little time.
 

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There is one more step you can do.

The throttle cable sheath ends at a bracket right by the APPS. You can take up the slack in the throttle cable by adjusting the nuts which clamp the sheath to the bracket. On both of mine, there was considerable slack, which meant the initial travel of the throttle pedal did nothing but take up the slack. After I adjusted it to remove the slack, the throttle felt much more responsive.

Unlike the APPS, the TPS requires careful mounting and calibration. The calibration procedure is detailed in the attached images from the service manual. Perhaps you should check the calibration of yours.
 

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UPDATE & SOS!

I have driven ~ 150 miles and there has no been any noticeable change.

While, i do not have the Toyota Handheld OBDII Scan Tool i did do the following:

I reinstalled the APPS to make double sure that it's installed correctly (it was) and i removed what little slack there was from the throttle cable. When the engine started, it idled around 1500 (vs ~ 1000 RMP prior). Attempted to spray carb cleaner in to the throttle body but the engine stalled the moment the air box hose was removed from the throttle body. Removed, cleaned the mass airflow sensor and reinstalled. No change, same 1500 RPM idle.

Lastly, i revisited the recently installed TPS. While i did not remove/reinstall the TPS, i did rotate it a tad but there was no change.

Should i double check the TPS installation? Is there another way to calibrate the TPS without the Toyota tool? I wonder if the OBDII scanner at the auto parts store can calibrate a Toyota TPS....?

Thanks for your advice so far!
 

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The two scans of the service manual that I posted earlier detail the calibration procedure. Calibration of the TPS consists overall of mounting it, rotating it to the proper position, and tightening its mounting screws. During the procedure, the ODBII scan tool lets you see the current, live throttle position ("THROTTLE POS") so that you can rotate the TPS to the correct position before tightening its mounting screws. This is not something the you can do correctly by any other method.

Any ODBII "scanner" can be used. Note that the simpler, cheaper ODBII tools can read and reset "check engine" codes, but nothing more. The "scanner" tools can also display current live engine parameters, such as the "THROTTLE POS" value, which is the current position of the throttle butterfly as a percent of full throttle. The instructions for the scanner show how to select and display such a parameter.

When you "did rotate it a tad", you messed with its calibration. You need to use a scanner, which you can borrow or rent from O'Reilly's (or other auto parts store), and use it to calibrate the TPS properly.
 

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I'm beginning to have trouble today with higher than normal idle speeds on my 2000 Tundra. It's good to see that DJ is still here and providing helpful information to keep these "old trucks" on the road! Now need to go see if I have any pending codes that will help me figure out my next step. Thanks again for these useful threads and this site that Lon started for us so many years ago. - Bob
 

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A scan didn't show any codes, but did notice some of the Readiness Test's weren't complete. My first thought was something had reset the ECU and it was having to go through a re-learn process. It turned out that the cause was the PWR-CUT switch for the Unichip had somehow got set to the OFF position, which causes the ECU to reset on every drive cycle. Had this happen in the past, but had me worried for awhile. Truck is now back to it's normal behavior, and all is good! - Bob
 

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I have a 2000 Tundra 4.7 with 175K on it was it running great! Driving in traffic the other day and i realize that i have no gas peddle response...D'OH! I know, sounds familiar from other threads but bear with me. All gauges read normal, trans is in "D" and zero throttle response! Put'er in neutral and push the gas and get nothing. Push harder and WAM...POWER! Later, i read out the code (P0120?) which says "...error throttle position sensor...". I've replaced the TPS and no change. Removed positive batter cable to reset ECM but no change. I did notice that in actuating the throttle cable assembly side that the throttle body does not open until just about at the end of its travel and the throttle body "butterfly" is not 100% at the end of its travel (actual throttle position just like the gas peddle). More interestingly is that i cannot make the butterfly open 100% from the passenger side (throttle cable side). I can make the butterfly open 100% from the TPS or drivers side. Weird that i get different ranges of butterfly motion from opposite sides.

Opinions, please? Do i have a bad APPS or Throttle Control Motor (TCM)? Or...?
So Mike, did you get it fix?? I’m having the same problem and can’t find a solution....
 
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