How does this Electronic throttle body work?

[fridaypassion]

This is a TB from a Toyota 2ZZ Fly by wire. Its becoming a slightly more common issue to get them faulting on the cars and stalling at idle. They are quite hard to find so I thought I would take a faulty one apart to see what was inside and was surprised to see that although its on a 6 pin plug with multiple wires on it the only internal connection appears to be these two connections to a motor. The "rest" position leaves a small gap on the butterfly there is no wear or anything inside it causing a mechanical issue so I assume that the issue is electronic. There's a mechanical stop there you can see but this the motor has to engage to get the butterfly to close which I assume it must be doing to get the stall. There is no external TPS sensor.

If its an issue with the motor I was wondering if we could swap the motor out with a more readily available toyota TB? There are lots of similar ones but they always have inlets smaller than the 72mm this one is.

[Studio263]

The motor is a DC brush type, it opens the throttle by turning the gear against the spring. By pulsing the motor on and off rapidly for a controlled amount of time you can get the throttle to open as much (or as little) as you like and stay there. You can sometimes hear the whistle of the rapid pulsing of the drive (it is called a 'variable mark/space ratio') when you turn the ignition on without starting the engine.

All this depends on the characteristics of the motor and the spring being accurately known. Things go wrong when the motor wears, the spring gets weak or friction builds up elsewhere in the mechanism. The motors are of a special type which is designed to stall, a normal motor would quickly burn out if used like this. A similar sort of thing is used in diesels where a throttle flap is used to quickly stop the engine when it is switched off. In this case the motor drives the throttle fully open when the engine is started and holds it there. When you turn the key off the spring pulls it closed again.

[stevieturbo]

rest position is more of a failsafe get you home sort of thing. The engine will run, maybe at a high idle at best.

6 wires is simple. 2 for the motor, 5v, gnd and 2 signal wires for the position of the blade.

As said above, the motor is driven open/closed very fast to maintain any perceived static position and at a high frequency pwm, or move open or closed as needed.

What is the mode of failure ?

[fridaypassion]

There are only 2 electrical connections in the TB the ones on the pic despite the 6 wires on the plug. Its odd! The fault is intermittent stalling when hot. the butterfly isn't fouling the housing from what I can see.