MOTOR Magazine

A MOTOR Magazine Newsletter
April 4, 2016

Contributed by Ryan Kooiman, Standard Motor Products Inc.
New Throttle Body Service Opps

Throttle body improvements provide new service opportunities

Throughout the years of internal-combustion gasoline engines, the main responsibility of a throttle body has been to contain the throttle plate (or blade), which is a device that controls the amount of air allowed to enter the engine. The same holds true today.

"In essence, an internal combustion engine is an air pump," explained Ryan Kooiman, Director of Training for Standard Motor Products Inc. "The more air that enters and exits the engine, the more power/torque is generated in the engine. The throttle body is the primary gatekeeper of how much air is allowed to enter the engine." Kooiman then described the evolution of throttle bodies and some new service opportunities that have emerged.

By leveraging new technologies, automakers now use electronic throttle controls, or "drive-by-wire" systems, which takes the direct throttle control away from the driver and gives it to the powertrain control module (PCM). (Image — Standard Motor Products)

Traditionally, the throttle plate has been connected to the accelerator pedal (or gas pedal) via a cable. If the driver wants to go faster, they press the pedal, which in turn pulls the cable and opens the throttle plate to allow more air to enter the engine. Likewise, if the vehicle is equipped with cruise control, it has another cable connected to the throttle plate and the cruise control servo.

In addition to a throttle plate, the throttle body contains an idle air control (IAC) valve, which allows air to bypass the throttle plate and control the vehicle's idle speed. When open, the IAC allows more air to enter the engine, which raises the idle. When closed, it decreases airflow and lowers the idle speed. Monitoring all of the throttle movement is a throttle position sensor (TPS).

Due to new technologies (such as hybrid vehicles and electronically controlled diesels) and the need for reduced emissions and increased efficiencies, manufacturers started using electronic throttle controls, or "drive-by-wire" systems. The system takes the direct throttle control away from the driver and gives it to the powertrain control module (PCM).

A Simpler Process

The process is simpler with electronic throttle control (ETC). To make a request, the driver simply presses on the accelerator pedal (APP), which is essentially a spring with several built-in position sensors. The PCM then analyzes inputs from various systems and sensors on the vehicle (transmission, traction control, engine temp, engine load, etc.) and sends a command to an electric motor in the throttle body, placing it at the desired position.

The position is determined by one of several throttle position sensors built in to the unit. The TPS reports the position to the PCM, which then adjusts the system accordingly. Benefits of ETC systems include powertrain protection, better control, driver comfort and component reduction, as there is no longer a need for a throttle cable, cruise control servo, or idle air control valve—the PCM and the throttle body motor can handle all of those functions now.

New Service Opportunities

With improvements and changes come new service opportunities, because the new systems have their own problems that can be troublesome for drivers and frustrating for technicians. Common concerns from drivers include illuminated CELs and vehicles stuck in limp mode.

When a vehicle is receiving a new throttle body, it is very important for the technician to look up the proper service procedure to do the idle relearn after the job. (Image — Standard Motor Products)

Those faults may occur for only a few milliseconds, but the symptoms can last for an entire drive cycle, making them difficult for a technician to pinpoint. For instance, does the fault code indicate a problem with a TPS or the engine wiring harness? Is the fault due to an electric motor or a wiring problem somewhere? Is there a software update available for the vehicle? The technician must answer all of those questions for a proper diagnosis.

Once the technician determines the need to replace the throttle body, they must use caution when installing the new one. For example, they must install the new gaskets or seals to prevent vacuum leaks, and torque the nuts and bolts to ensure a tight fit. Most important, the technician needs to follow the manufacturer's instructions regarding idle relearn.

Not All Relearn Procedures Are Alike

Many manufacturers have a straightforward procedure that involves clearing the PCM's memory (previous idle conditions and fault codes), then starting the engine and allowing it to idle for the following durations:

  • Two minutes in park with the A/C off.
  • Two minutes in park with the A/C on.
  • Two minutes in gear with the A/C off and a foot on the brake.
  • Two minutes in gear with the A/C on and a foot on the brake.

The process should be followed by a test drive (possibly including several closed throttle decelerations) to verify that the vehicle is repaired properly and doesn't stall at idle.

Note that some manufacturers have a more involved process. Nissans from the late '90s and early '00s are one example. Their process seemingly requires the technician to do the hokey pokey, making him jump up and down on his left foot, hold his breath, and rub his left hand on his head. If the complicated process isn't followed with 100 percent accuracy, the vehicle will not idle properly and/or turn on the CEL.

The Takeaway

Regardless of which vehicle is receiving the new throttle body, it is very important for the technician to look up the proper procedure to do the idle relearn after the job.

[Editor's note: For the latest diagnostic and automotive service insights, read MOTOR Magazine's March 2016 issue.]

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