Toyota Throttle Bodies and Throttle Position Sensors
By Jim Brink
(toytech@off-road.com)

This article will cover what the throttle body does, how the TPS works, and how it can be inspected and adjusted.

What they are: The throttle body is the heart of the induction system of any fuel injected engine. Like a carburetor, the throttle body's function is to introduce air to be mixed with fuel for the combustion process. Toyota throttle bodies contain the throttle valve (butterfly or throttle plate), an air bypass passage to regulate idle speed, vacuum ports for vacuum accessories, and the throttle position sensor or TPS.

The throttle linkage is attached directly to the throttle valve on one side of the throttle body. On the other side of the throttle body is the throttle position sensor. The TPS is used to supply the ECU (Engine Control Unit or computer) with critical information such as idle status and driver demand. Think of the TPS as a sophisticated accelerator pump in a carburetor. The TPS informs the ECU when the engine is at idle, when the driver opens the throttle, how much the throttle is opened, and how quickly. The computer uses that information to make adjustments to fuel delivery and spark advance. From an emissions standpoint, the TPS can also shut off fuel to the fuel injectors when it senses the throttle closing quickly while the vehicle is in motion (from which other sensors are employed) so that the engine is not flooded with fuel as the intake air is suddenly turned off. This results in a drastic reduction in raw hydrocarbon emissions (HC) or unburned fuel.

How it works: Most Toyota trucks with either the 22R-E, R-EC, R-TE, or 3VZ-E engines use what is known as a "Linear" throttle position sensor.The linear type sensor basically looks at idle or closed throttle (IDL) and throttle angle opening (VTA). The TPS works on a 0-5volt range, 0 volts being idle and up to 5 volts representing throttle opening angle.This is acomplished by the TPS being connected directly to the throttle plate and within the TPS is a sliding resistor that moves along contact points, closed throttle, varying voltage, and full 5 volts indicating wide open throttle. Proper adjustment of the TPS is critical for engine performance, fuel economy, and emissions. An improperly adjusted TPS effects many other inputs and outputs from the ECU, many of which would not even logically point to the TPS. Aside from being out of adjustment, the TPS can just plain wear out or break internally.

Maintenance and Service: Periodically, the throttle body should be cleaned or checked for a buildup of sludge that may clog the air bypasses, vacuum ports, or prevent the throttle plate from closing to it's proper position. This should be checked prior to any adjustment of the TPS should a trouble code relating to throttle position appear during a self-diagnostic test. Crankcase vapors are commonly vented into the throttle body for re-intorduction into the combusion process. These vapors can leave an oily residue on the back of the throttle pate and allow sludge and dirt to accumulate. The throttle body can easily be cleaned while on the vehicle with a little carburetor cleaner and a cloth. However, for heavy sludge buildup, it should be completely removed, washed in solvent, and dried thouroughly. When doing this, the TPS should be removed to prevent contamination and the throttle body-to-plenum gasket replaced.

Adjustments and diagnosises: Adjusting the throttle body takes just a few minutes and no specialized tools.

Symptoms, do's and dont's: Symptoms of a bad or mis-adjusted TPS include variying idle speed, hesitation while accelerating, poor fuel economy, and inabiltiy to correctly set base ignition timing.

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