The throttle body contains a single throttle valve which controls the
amount of air delivered to the engine. A coolant passage under the throttle
valve heats the throttle body.
The Throttle Position (TP) sensor and Idle Air Control (IAC) valve are
mounted on the throttle body. The TP sensor and minimum air stop are not adjustable.
The TP sensor is a potentiometer that is mounted on the throttle body
and provides the PCM with information on throttle valve angle. The PCM provides
a 5 volt reference signal and a ground to the TP sensor and the sensor
returns a signal voltage that changes with throttle valve angle. At
closed throttle (close to 0 degrees) the TP sensor output signal is
low (below 1 volt) and at WOT (greater than 80 degrees) the TP sensor
output signal is high (above 4 volts). Because the TP sensor is not
adjustable, the PCM must account for build tolerances that could affect
the TP sensor output at closed throttle. The PCM uses a learning algorithm
so that it can correct for variations of up to 6 degrees of throttle
angle.
The PCM uses TP information to modify fuel control based on throttle
valve angle. For example, power enrichment occurs when the throttle angle
approaches WOT. Acceleration enrichment occurs when the throttle angle
increases rapidly (similar to an accelerator pump on a carburetor).
A faulty TP sensor may cause various driveability conditions and should
set a DTC.