Throttle Plate Control

David Cooley cooldave at
Fri May 12 01:21:11 GMT 1995

>As I recall, the ZR-1 has dual runners going to each port.  There is a
>butterfly valve in each secondary runner which is opened by a motor at
>the PCM's command for WOT operation.  If you are using the valet key,
>the secondary butterflies are not commanded open, significantly reducing
>airflow.  This is not quite the same thing as a "secondary throttle
>plate", but perhaps it's what Lou is talking about.
My 93 Jimmy with the HO 200HP 4.3 had this too... Only it was a Plenum divider
in the manifold that over a certain throttle position and RPM, flipped open
and connected the 2 halves of the plenum for top end power.

>At the Detroit Auto Show in January I observed the Lexus 4.0l motor had
>two distinct throttle plates of identical size in series in the throttle
>body, the second apparently actuated by a servo, the first mechanically.
>It appears that engine has a true secondary throttle plate.  I have no
>idea what it is for, but I'm guessing idle control at the very least.

That is their traction control.. I have a friend Who works for Lexus in the
port of Los Angeles going over the electronics after they come off the ships
to make sure they are ok.  Most traction controls use a servo that actually
tries to force the main throttle closed... You can feel it in your foot when
the tires spin... the pedal pushes back... The lexus, uses a 2nd throttle
plate behind (or in front of) the first main throttle... Normally, when the
car is running it is fully open.. If the PCM senses any wheel spin while the
traction control is engaged, it will shut that 2nd throttle plate down until
the spin stops.
David Cooley                                            (919) 319-2734 Office
cooldave at                                      (919) 319-2896 FAX
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