Throttle body injection troubleshooting

Written by tom lutzenberger
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The throttle body in a car provides the control of air and fuel injection so that the system runs efficiently and does not backflow. When this automotive part is not working correctly, or its electronic sensors begin firing off readings to the on-board diagnostic computer showing problems, it can create car problems. Not only does a malfunctioning throttle body have the capability to cause the check engine light to come on, it can also cause other sensors to overcompensate, causing other problems elsewhere. Typical related issues will include the oxygen sensor and the mass air flow sensor. As a result, automotive diagnostics of a troublesome throttle body can include a process of elimination with other parts as well.

Skill level:

Things you need

  • Shop-vac vacuum cleaner
  • New air filter
  • Mass air flow cleaner
  • Screwdrivers
  • Torque screwdrivers
  • Shop rag
  • O2 sensor tool
  • OBD scanner
  • Flashlight
  • Carb cleaner
  • Socket wrench and sockets
  • Crescent wrenches
  • New throttle body base gasket

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  1. 1

    Open up the car front bonnet and prop it up with the bonnet support arm to keep the engine area clear for working. Pop open the air filter box to pull out the old air filter. Use a shop-vac vacuum cleaner to remove all forms of debris caught by the filter. Replace the air filter with a new one. Close up the box.

  2. 2

    Disconnect the air intake hose to the mass air flow sensor by hand. Use a screwdriver to disconnect any securing clamp on the hose. Use a screwdriver or torque screwdriver, depending on the screw used, to detach the mass air flow sensor from the air box. Spray the sensor wires with mass air flow sensor cleaner and let dry sitting on a shop rag. Do not touch the wires with anything. Re-install the sensor, reversing the steps of this section.

  3. 3

    Go underneath the car near the transmission. Find the rear oxygen sensor on the exhaust channel. Use a crescent wrench or O2 sensor tool to disconnect it. Disconnect the sensor wiring from the car. Replace the sensor with a new one. Connect the new wiring. Get back up and use an OBD scanner to wipe the error codes from the car and start it again. See if the throttle body warnings come back when running the car.

  1. 1

    Locate the throttle body at the end of the air intake hose going into the engine block after exiting the mass air flow sensor. Use a screwdriver to disconnect the hose clamp. Pull the hose off the throttle body.

  2. 2

    Shine a flashlight if possible into the part to examine the carbon build-up on the inner body. Check that the throttle flap is not stuck open. Use a socket wrench and crescent wrench to loosen the bolts holding the throttle body to the engine block. Pull the unit off and disconnect the electronic sensor from the car wiring.

  3. 3

    Spray carb cleaner or similar solvent to breakdown the carbon deposits inside the throttle body and flap. Scrub the part with the plastic brush to avoid scratching the sensitive flap. Scrub until thoroughly clean. Let the body dry. Rebolt the unit the engine block with a new body base gasket in between. Reconnect the body sensor and the intake hose, screwing the hose clamp tight with a screwdriver.

  4. 4

    Wipe the error codes from the car with the OBD scanner plugged into it and test the car engine by running it to see if the check engine light and error codes reappear again.

Tips and warnings

  • Check out similar car forums on the Internet to get specific advice on how to deal with the throttle bodywork on your particular car. Details and locations of the throttle body can vary from brand to brand and model to model, depending on design. Also, note that different car designs position the filter box and parts in different locations. The trick is to find the air filter box. Everything to the intake valve will connect from there. Check with your car owner's manual if you're not sure where the box is in the engine.
  • Do not try to clean the throttle body while it is still installed on the engine block. You will just spray all your debris into the engine which can cause problem when it starts up later on.

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