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Discussion Starter #1 (Edited)
1. TA-1 with the circuit board off. Returns to starting point rather rapidly, no?
2. I've put small wire probes into the two connections on the circuit board. I then attach the alligator clips to the big flat connectors (to the motor) in the TA-1
3. I do the lever / gear thing AND LOOK HOW SLOW THE GEARS RETURN TO STARTING POINT.

All I can think of is that the capacitor in the circuit board cover has a charge and that it is affecting or activating the motor somehow - with the results that cause the errors on start up test due to the slow return.

+ https://www.youtube.com/watch?v=Ayekf_xSDCY" title="View this video at YouTube in a new window or tab" target="_blank">YouTube Video
https://www.youtube.com/watch?v=Ayekf_xSDCY"> https://www.youtube.com/watch?v=Ayekf_xSDCY" /> ERROR: If you can see this, then YouTube is down or you don't have Flash installed.


Now, can someone tell me how to pop the motor out? Why, if it's getting power, does the motor slow down the return? Is this more of a circuit board thing?

Will anyone answer this? Can anyone replicate this?
 

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Discussion Starter #2 (Edited)
Hmmm. A bunch of views and NO COMMENTS, no ideas, nothing? Don't you think that this is new and evolutionary information that could lead to an inexpensive solution to the Throttle actuator problem - especially if replacing gears doesn't work?

Even if this is the stupidest thing you've ever seen and I'm wrong wrong wrong with the idea that this is the cause of the problems (is this normal operating behaviour? Is this something that changing the gears will fix? (spoiler: no) - TELL ME.

C'mon give me an opinion.
 

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The reason for the TA to return to rest position slowly when connected to the (powered) PC board is that the H-bridge implements a short through the back gate diodes of the MOSFET. When the motor is shorted the back EMF generated in the motor as result of the spring driving it, causes a current to flow (which is shorted out). Rotational potential (spring) energy is converted to heat in the motor windings. Moreover it creates a magnetic field which slows the motor down. That is the reason for the slow return. Expected behavior. If you do not believe me, short the motor out on its terminals and you will see the same behavior.
 

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Discussion Starter #4 (Edited)
The reason for the TA to return to rest position slowly when connected to the PC board is that the H-bridge implements a short through the back gate diodes of the MOSFET. When the motor is shorted the back EMF generated in the motor as result of the spring driving it, causes a current to flow (which is shorted out). Rotational potential (spring) energy is converted to heat in the motor windings. Moreover it creates a magnetic field which slows the motor down. That is the reason for the slow return. Expected behavior. If you do not believe me, short the motor out on its terminals and you will see the same behavior.
I believe you. I tried it on TA-1 and not only is it slow return, but it is very hard to move the gear. SO what you're saying is that I have a short on that circuit board? Because I get the the throttles just springing back on TA-2 and it does the flickering when ISTA tests it.

How come my TA-1 works one minute and not the next? If this is indicative behaviour when the circuit is complete than how does the TA ever pass the pre-start test?
 

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No, MOSFETs block current only on one direction. There is an unintentional diode across them (internally) that causes the 'short'.

The intermittence is a result of the internals of the TA not passing some kind of self test. If it fails it throws an error status in the CAN response and turns into a vegetable until the next power cycle.
 

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If you want to remove the motor in the TA just remove the two screws that hold it in and put it face down and hit the back with a dead blow hammer or similar several times and it will fall right out.
 

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You want the motor to resist in powered (but closed) mode. The butterflies have to stay closed out of fail safe considerations. If you open the butterflies you would accelerate.
 

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Discussion Starter #10 (Edited)
Still. I have 2 TAs behaving differently. What you are saying is that the TA-2 which has no resistance is not working properly. Don't the throttle valves get held in position by their own springs? They're not going to pop open unless the motor is activated. And they have to return to closed fast - or else you would not have proper control when the foot comes off the pedal.

Maybe you should explain everything to me in baby steps, because clearly I am confused and don't understand.

TA-1 which is out of the car, shows no resistance when the circuit board is off. When the circuit board is on, it shows only resistance to returning to rest (throttles closed). When I short across the motor terminals, with no circuit board, it has great resistance in both directions. Resistance here being of the mechanical kind, not electrical.

TA-2 which is in the car - when I open all the throttles manually, they spring back closed instantly when I release the lever. (Unlike TA-1, which when in the car would see the throttles on that bank close slowly - twice as slow - when opened manually like I ddid for TA-2. Different behaviour from the two throttles in a shut off cold car. :(

In any case, I've ordered a new one (VDO) from Spareto.com (european) for quite an attractive price given the cost over here in NorthAm. :)
 

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Discussion Starter #11
No MOSFETs block current only on one direction. There is an unintentional diode across them (internally) that causes the 'short'.

The intermittence is a result of the internals of the TA not passing some kind of self test. If it fails it throws an error status in the CAN response and turns into a vegetable until the next power cycle.
Great. The insane TA is judging itself. Some weed those BMW engineers must have been smoking that night.

So when everything works and the car comes up in ignition 2 (not running but ignition on), something happens between then and the next time I turn it on.

I had both TAs opening fine with the component test (the 20 second one). TA-2 would snap shut, but TA-1 would drift shut and lead to the limp mode. Why is this? What would cause the motor to provide resistance like that in one TA and not the other?
 

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From you description in your latest post it indeed appears to me that TA-1 is broken. You say it resists when it is connected to the circuit board but it is NOT powered. It should only resist when it is powered ON. Essentially, when the TA is CLOSED, the power electronics connect each of the terminals of the motor to ground/negative. So, by doing so, they are also connected together and thus shorted. When the TA is NOT powered, the circuit electronics and thus the MOSFETs are not driven and are an open circuit. It becomes a high impedance (disconnected) connection as long as the motor terminal voltage stays below 1.4V (2 diode drops). There will be no motor resistance. When the voltage spikes above 1.4V there will be motor resistance as the (unintentional) diodes start conducting, forming a short. But once the voltage drops below 1.4V, resistance goes away. Overall you would expect less resistance when not powered.

If you say TA closes slowly when NOT powered you either have a circuit board short (very likely broken MOSFET(s)) and/or a mechanical problem.

Here is a video of my setup that shows it all one more time in action. Notice that my TA is notchy near its closing position. A mechanical issue! This is what it produced my TA errors. In this case, it is a combination of worn gears and the need for lubrication.

https://vimeo.com/171674813

Most ECUs these days runs hosts of self-tests and are able to "judge themselves" to great extend. This is what the OEMs require, not just BMW. That is a good thing. Try to debug this issue considering you have no fault codes. Where do you start in these systems. Very obscure issue at that point.

If you are up for it, send me your broken TA for more analysis. Send me a PM.
 

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Discussion Starter #13 (Edited)
Yes. It resists when connected to the circuit board and there is no power. It double resists when a short is applied across the motor terminals. TA-2 is great though. When running the valve test through the ISTA "test plan" on throttle valve actuator error codes, the butterfly valves flap easily and everything passes. TA-1 just sits there stunned. But when I first put it back in, everything worked fine. It was only when I ran the Component triggering in ISTA that everything went south. All throttle valves opened fine. TA-2 slammed shut at the end of 20 seconds. TA-1 drifted (relatively) shut. Then I got the error codes again.

That is when I started the investigation and stumbled upon the resistance of the motor/gears in the TA to returning to 'rest' position (closed on the throttles) when the motor contacts were connected to the circuit board with NO power.
 
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