Throttle Actuator failure modes and codes

[Tony B]

I am trying to diagnose what I believe is a throttle actuator problem, but without error codes my dealer will not replace under warranty.

Long post...sorry..

There are 2 symptoms which I can detect:

a) a slight unneveness/hesitation at 2.2k revs/constant speed. It is not so strong that I would describe it as a misfire, and as soon as I open the throttle it disappears
b) very "soggy" response to accelerator movement from the fully closed position - this is really noticeable when attempting to throttle blip on down changes. This even applies when I am using the most aggressive throttle map. It is also even noticeable on gentle up changes. At all other times the engine is really responsive to throttle inputs, and always has been.

So...eventually...my questions

TA failure modes and error codes (or lack of).

1. Electronics (PCB) - if there is a problem here it would surely be sufficient to trigger an error code? And it would also be consistent, either working properly or not working at all?
2. Electrical (the actuator motor) - could there be a "soft" degradation here, which would not trigger a code? This could explain the "soggy" throttle response to blipping.
3. The actuator cog (mechanical) - I know the plastic part wears, and this wear would probably happen more in the sector that gets used most - at or near closed throttle. This could lead to some throttle butterfly backlash in some circumstances (my constant speed 2.2k revs situation?). How much cog wear is necessary for codes to be triggered?

How does ISTA check throttle actuator health?
Does it perform a sequence of static tests at various throttle openings, or is it capable of doing dynamic/transient performance tests?

TIA!

[spammysammich]

Is your car modded?

[omgzirra_exe]

just drive it until the code comes up, it'll be stored and will keep coming back. and yes ista does a TA test, its a TA-precheck basically.

just keep doing full wot pulls and it will throw the code eventually since it needs voltage to hold the throttle linkage open.

[Tony B]

Originally Posted by spammysammich

Is your car modded?

No way!

Absolutely standard, and full (extensive) service history from new (I am the only owner).

49k miles, 2012 MY, and from memory the ECU has the latest software.

As it is still under warranty, anything that has needed replacement has always been replaced, but lately BMW (or their warranty administrators) have been getting very reluctant to cover stuff, unless there are fault codes present.

[Tony B]

Originally Posted by omgzirra_exe

just drive it until the code comes up, it'll be stored and will keep coming back. and yes ista does a TA test, its a TA-precheck basically.

just keep doing full wot pulls and it will throw the code eventually since it needs voltage to hold the throttle linkage open.

Is the TA pre-check from 0 to 100% opening without running the engine? So just checking that full range of movement is available?

Full WOT pulls to maximum revs (in lower gears), or use 6th gear to get a longer time at WOT? Even in 6th gear, it does not take long to get to licence shredding speeds in the UK

I have not taken it on an autobahn for too many years - I think 2017 or 2018 was the last time!

(must check my videos)

[omgzirra_exe]

Originally Posted by Tony B

Is the TA pre-check from 0 to 100% opening without running the engine? So just checking that full range of movement is available?

Full WOT pulls to maximum revs (in lower gears), or use 6th gear to get a longer time at WOT? Even in 6th gear, it does not take long to get to licence shredding speeds in the UK

I have not taken it on an autobahn for too many years - I think 2017 or 2018 was the last time!

(must check my videos)

Yeah, pretty much, it just opens and closes the throttle bodies before starting up. Just leave your foot off the brake if you're in DCT or off the clutch if you're in a 6-speed. You will hear the TA open and close.

If you use ISTA, there is a procedure that it runs through with the car in ignition mode, which would give you exact numbers, but won't really indicate failure per se.

I think a few 2-4th pulls would help.. you really want to get temperature into the TA for it to overheat and basically fail.

[Tony B]

Originally Posted by omgzirra_exe

Yeah, pretty much, it just opens and closes the throttle bodies before starting up. Just leave your foot off the brake if you're in DCT or off the clutch if you're in a 6-speed. You will hear the TA open and close.

If you use ISTA, there is a procedure that it runs through with the car in ignition mode, which would give you exact numbers, but won't really indicate failure per se.

I think a few 2-4th pulls would help.. you really want to get temperature into the TA for it to overheat and basically fail.

I assume that the throttle position achieved during the test will basically be determined by the actuator/motor shaft position achieved, as there is no sensor which detects the actual position of the butterflies themselves? So wear in the plastic gear will not be detected this way?

Happy to try the pulls - somewhere quiet, and legal of course ;-)

I can see that I might end up removing the plenum to check for backlash in the actuator gears, which is going to be a pain..

[omgzirra_exe]

Originally Posted by Tony B

I assume that the throttle position achieved during the test will basically be determined by the actuator/motor shaft position achieved, as there is no sensor which detects the actual position of the butterflies themselves? So wear in the plastic gear will not be detected this way?

Happy to try the pulls - somewhere quiet, and legal of course ;-)

I can see that I might end up removing the plenum to check for backlash in the actuator gears, which is going to be a pain..

plastic wear will not be detected.

you can watch this video.

https://www.youtube.com/watch?app=desktop&v=iP7Mw3w3Z2o

[Tony B]

Originally Posted by omgzirra_exe

plastic wear will not be detected.

you can watch this video.

https://www.youtube.com/watch?app=desktop&v=iP7Mw3w3Z2o

Thanks for sharing this - I had actually watched it before (my comment is at the top of the list...brainfade on my part, duh).

I suppose that I might be missing a problem at the accelerator end - there must be a potentiometer or optical position reader there to get the demand side of the process.

Must find someone local with ISTA, who does not charge £210/hr...

[Tony B]

Originally Posted by omgzirra_exe

Yeah, pretty much, it just opens and closes the throttle bodies before starting up. Just leave your foot off the brake if you're in DCT or off the clutch if you're in a 6-speed. You will hear the TA open and close.

If you use ISTA, there is a procedure that it runs through with the car in ignition mode, which would give you exact numbers, but won't really indicate failure per se.

I think a few 2-4th pulls would help.. you really want to get temperature into the TA for it to overheat and basically fail.

Originally Posted by omgzirra_exe

Yeah, pretty much, it just opens and closes the throttle bodies before starting up. Just leave your foot off the brake if you're in DCT or off the clutch if you're in a 6-speed. You will hear the TA open and close.

If you use ISTA, there is a procedure that it runs through with the car in ignition mode, which would give you exact numbers, but won't really indicate failure per se.

I think a few 2-4th pulls would help.. you really want to get temperature into the TA for it to overheat and basically fail.

Thread resurrection.

I tried the "ignition on" actuator test, for throttle movement, using a GoPro wedged into position (on one bank, no room on the other bank).

The only movement was a momentary "twitch" of the actuator, nowhere near a full movement from zero to 100% throttle. I would guess at no more than 5% of full range.

The twitch occurred on ignition switch off, too.

If that is the full actuator test, it's a bit rubbish!

And is it any wonder that these actuators wear out so quickly with this "test" every time you switch on, or off.

[

[omgzirra_exe]

Originally Posted by Tony B

Thread resurrection.

I tried the "ignition on" actuator test, for throttle movement, using a GoPro wedged into position (on one bank, no room on the other bank).

The only movement was a momentary "twitch" of the actuator, nowhere near a full movement from zero to 100% throttle. I would guess at no more than 5% of full range.

The twitch occurred on ignition switch off, too.

If that is the full actuator test, it's a bit rubbish!

And is it any wonder that these actuators wear out so quickly with this "test" every time you switch on, or off.

I will try to post to YouTube later today

yea it's best to use bmw tools for this one. wont really tell you if it's failed though.