Secondary throttle plate sticks closed, feels like a detent. How to fix?

[pentiumbased]

Hi all, I posted about this lasted month on bimmerforums for my US E36 318i, but got no responses. I thought I'd have better luck in a forum more dedicated to the m42, especially since (to my knowledge) only the m42/44 has this style of throttle body, and since E30 owners seem to be more enthusiastic about this engine in general.
I think the throttle body is different on the E30, but mechanically it should be the same as the one on the E36, going off of pictures online.
Below is mostly copy pasted from that old thread:

The secondary throttle (the bigger one) on my 94 318i is hard to open when it's fully closed. It feels like a strong detent in the middle of accelerator pedel travel, like the feeling of metal stiction breaking downstream of the pedal.
It takes mild to quite heavy pedal pressure to unstick it. Sometimes it's very stuck and other times it barely sticks. When it's very stuck, my fingers are not strong enough to move it manually in the engine bay.
It will stick again every time it closes. The primary is fine all the time, and after the secondary is unstuck, it feels normal until it closes again.
Letting it close softly vs. snapping the throttle shut makes no difference.
It makes throttle control for any acceleration beyond "leisurely" quite difficult.

I'd like to ask those who have looked closely at the dual-stage throttle body of the M42/44 for some insight on how to fix this. That way I'll have less chance of breaking it when I take it out to mess with it.
I will also take this chance to ask if the throttle cable is ever worth replacing. Mine feels alright, but I've been spoiled by DBW so I don't know what a good cable throttle is supposed to feel like.

Thank you

[roguetoaster]

Start with disconnecting the cable(s) at the TB. Then move the TB by hand, which will tell you if it's cable or TB.

If cable, replace, and they do go bad.

If the TB, it's not really serviceable, so I'd opt for a used unit. If you still have the TB preheaters in place (can't recall if E36s have them anyway) it makes removing the throttle assy difficult, but achievable. If you end up removing it from the car, be careful with those hoses.

The service you can do on your TB if required is just clean/lube it. Mostly at the plates (remove the intake boot to inspect), and at the return spring assy.

[pentiumbased]

Start with disconnecting the cable(s) at the TB. Then move the TB by hand, which will tell you if it's cable or TB.

If cable, replace, and they do go bad.

If the TB, it's not really serviceable, so I'd opt for a used unit. If you still have the TB preheaters in place (can't recall if E36s have them anyway) it makes removing the throttle assy difficult, but achievable. If you end up removing it from the car, be careful with those hoses.

The service you can do on your TB if required is just clean/lube it. Mostly at the plates (remove the intake boot to inspect), and at the return spring assy.

The cable does not move with the linkages if the linkage is moved by hand. It feels and sounds like metal-on-metal stiction breaking loose.
When I had the intake boot off to look inside today, the timbre of the sound changed to a more reverb-ey and metallic one, suggesting that the sticking point is coming from inside the TB.
I think the secondary butterfly plate is sticking against the bore. I applied Vaseline to the lower inner edge of the butterfly, which helped temporarily, but it might have been a fluke.
Is the butterfly hitting the bore the way it's meant to rest/stop? I didn't see any lip on the bore where it could rest, but I wasn't looking very closely because I didn't have the boot all the way off.
Is there a way to make the secondary sit ever so slightly more open like you can with the stop screw on the primary linkage?

[roguetoaster]

Take the throttle cable off, inspect and operate just the throttle by hand while looking at the butterflies.

Most likely, the bushing that the throttle shaft rides in is worn out. That's accelerated by a bad cable or lack of free movement in the progressive linkage.

[Jordan]

The issue that causes the problem you have is in the linkage itself, or the bushings, corrosion has worked its magic and caused the bushing to cut into the shaft. Long story short its a parts unit at this point, it will need parts you can't buy to fix it, so its a donor for another...

I refurbish these to the expected standard, along with all other E30 throttle bodies. New bearings, seals, vapor honed, plated etc etc. Smooth as butter and looks better than new. M42 units aren't on my web store yet, but will be soon. If you want to smack the east button and buy one that is like new while sending yours in as a core let me know.

[TobyB]

First, have you cleaned the larger bore? This is a classic symptom of carbon buildup inside there.

Second, as Jordan asks, have you checked for bushing play? It's unusual for the secondary to wear,
as it only opens at 70+mph, and thus doesn't get lots of small, frequent adjustments on an E36- those
movements that will wear it out.

Thoid, have you made sure the throttle plate itself is secured to the shaft? If the screws loosen even slightly,
it will stick.

Fourth, there is a procedure to re- center the throttle plate in the bore. It can be a real pain in the butt.
At which point, a spare throttle assembly is easier. Or at least, good to have as a backup. M42s are still
showing up in the yards around me...

I went out and looked- on the later E36 M42, anyway, there doesn't appear to be a closure stop on the secondary.
Which seems really odd, as it seems like the plate would wear into the bore. However there IS a
'force closed' nub on the primary linkage- on mine, that nub stops maybe half a mm from pushing down on
the secondary linkage. If yours was adjusted (or worn- that engine has 220k and no appreciable shaft bore wear)
such that the 'force the secondary closed' nub was pushing on the secondary linkage, THAT might cause
binding...

all I got,
t