Throttle Plate Control

Ed Lansinger elansi01 at
Fri May 12 00:01:49 GMT 1995

Lou Faustini wrote:

>    Didn't the Corvette ZR-1 use a servo-motor to control the _secondary_ set
>of throttle plates?  

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.

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.
The motor also has twin distributors!  Imagine that in this day of
direct ignition.  Must be their secret to high CAMIP and J.D. Power
ratings.  Of course, they all run and hide when I meet them at the

Ed Lansinger
General Motors Powertrain
Powertrain Control Center
Premium V Software & Calibration Group Northstar/Aurora
Milford Proving Ground, Milford, MI
elansi01 at  8-341-3049  (810) 684-3049

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