High idle, sticking throttle, throttle body questions

SJ syljay at optonline.net
Wed Oct 1 20:02:26 EDT 2003

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

2. Unintended acceleration: After pressing the gas pedal past a certain
point (secondary throttle valve activation), the throttle wont return.
Noticeable on shifts - the RPM's climb to 5k.
Letting out the clutch will reign in the RPM's, but sometimes the throttle
is stuck until you stomp on the gas pedal to release the throttle. Thats a
bit scary.

I tested the ISV valve. Unplugged the electrical connection . .no change in
idle. I pinched off the hose . . no change in idle.
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.

Now the questions:

1. Idle switch - I read 8.0 ohms instead of 0.0 with contacts closed. The
reading is consistent. I read in the archives about cleaning out the
contacts by drilling a small hole in the switch body and spraying in contact
cleaner. How effective is this procedure? Does the idle switch ground a
circuit or provides voltage to a circuit?

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?

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.
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?

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.
I suspect that the set screw described above in #3 actually is the positive
shut-off for the secondary throttle plate. Otherwise any minor binding of
the secondary shaft would result in a slightly open throttle plate . .which
gives higher idle RPM.

85 Dodge PU, D-250, 318, auto
85 Audi 4k - - sold but still on the road
88 Audi 5kq
90 Audi 100q

More information about the quattro mailing list