High idle, sticking throttle, throttle body questions

[Huw Powell]

> Keywords: high idle, unintended acceleration
>
> Patient is a 1990 100q     non turbo, manual transmission
>
> Here are the problems I am experiencing.
>
> 1. Idle is at 1200 rpm

> I traced the problem to the throttle body. There is friction in the moving
> parts and the secondary throttle plate does not close completely. The
> primary throttle plate closes ok.

my coupe did this once, though it was stuck at 3k.  Which was an awful
way to drive til I got home.  Pull big rubber boot off throttle body and
clean and lubricate every moving part you can get to.

> 2. What is the purpose of the dashpot? I know it slows down the closing of
> the primary throttle plate at the end of its travel by about 1.5 seconds.
> Why is it necessary?

I think I almost figured that out once.  Removed mine, noticed no
difference.  I suspect it might be to lower emissions, or *perhaps* to
improve driveability a tiny bit.

> 3. The adjusting screw in the primary/secondary linkage has no head. It
> looks like the head was sheared off deliberately after the factory assembled
> and adjusted the linkage.

Sounds about right.  The throttle body is *one* part in the FA.  Most of
it isn;t really designed to come apart, although with a little coaxing
it can be done.  Just take pictures first!

> The function of this screw appears to provide a positive mechanical stop to
> ensure that the secondary is completely closed when the primary is in idle.
> A lever on the primary shaft presses against this screw stop. The screw
> intself is mounted on the lever mechanism for the secondary.
> I have about a .020 gap between the screw and the lever. The only thing that
> shuts off the secondary completely is a small spring at the end of its
> travel . . .not much leverage there.
> I have to figure out a way to make an adjustment . .I may just grab the set
> screw with pliers. Any ideas?

Yes, clean it.  Most of these TB's have big springs wrapped around the
bottom of the butterfly "axles" that will close them just fine.  Clean
them...

> I stepped away from this email and did some more cleaning and lubricating on
> the throttle shafts. I used WD-40 on the shafts and linkages.
> I got the secondary shaft and linkages freed up . . .the plates now close
> under spring tension only.

Uh, ok, well, I guess all the times I said "clean it" above are now
redundant...

--
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/