[DJ]

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.

 

[DJ]

It is not nice to know that the replacement part is ~ $300 and not widely available from my usual sources (e.g. Amazon, etc.).

I noticed that, but the OEM part lasts a very long time, and it is one part that you don't want schizophrenic behavior from.

 

[DJ]

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.

 

[DJ]

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.