High idle problem, symptoms and the fix

[SJ]

Patient:
1990 100Q, 5 cyl, non turbo, manual

Symptom:
High idle
engine idles above 1100 RPM
when letting off the gas at certain speeds/rpms, it seems like the engine
power stays on before reducing in synch with the gas pedal

Solution:
The symptoms were caused by sticking levers controlling the secondary
throttle plate in the throttle body

The throttle body has two throttle plates . . looks like a two barrel carb
setup.
The secondary plates are mechanically actuated via levers and hinge points
by the throttle mechanisms.

The secondary plate levers rust and bind - similar to rusty scissors. This
binding prevents the secondary plates from closing completely and hence you
get high idle.

The fix was scraping away the rust from the levers and filing smooth the
lever surfaces. A good soak in Kroil oil penetrant loosened up the hinge
points.
I've been adding a drop of Kroil oil to the lever hinge points(2) once a
week. That keeps the hinges lubricated and keeps the levers coated with oil
to prevent further rusting.


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




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