Throttle Body Butterfly Bushing/Seal Wear - BMW R850 Maintenance Manual

Throttle Body Butterfly Bushing/Seal Wear - Rob Lentini
Problems with throttle body synchronization and accomplishment of "zero=zero"
may, but rarely, be caused by wear or failure of the throttle butterfly shaft
bushings and/or seals. While these parts are not currently available for
replacement (though may be shortly), here's how to tell if you have this rare wear
problem:
Spray carb cleaner, propane, or simply WD-40 at the throttle shaft pivot area with
the engine running and listen for RPM speed-up. These bushings/seals are
located just outside of the cable wheels on each throttle body—the arcing
grooved wheel that encloses the throttle cable for each cylinder throttle body.
The area to be sprayed is between the surface of the cable wheel and the
throttle body casting. When spraying, avoid the intake of the air box "horn" on
the left side of the engine or you may get false RPM increases from inhalation of
the solvent into the air box.
A speed-up indicates the solvent is being "vacuumed" past a bad bushing and/or
seal and is being pulled into the cylinder as more "fuel." Try this procedure at
idle and at, say, 3000 RPM to pick up rotational differences of the throttle shafts.
If you detect RPM increase you have little recourse other than a warranty claim
or throttle body replacement at your expense. Subsequent parts availability may
soften this expense in the future.
Editor's Note: You might also experience an increase in RPM if you have an air
leak at the large hose clamps - front and back of the throttle bodies (especially
the front clamp). So avoid spraying there when checking the butterfly seal or
better yet, check them by spraying before you do the above procedure and
tighten the hose clamps if necessary.
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