The throttle body is the valve between the air intake and the intake manifold that controls how much air enters the engine. Pressing the accelerator opens its throttle plate; on most modern vehicles an electric motor opens it (electronic throttle control, or drive-by-wire) based on the pedal position. A dirty or failing throttle body causes a rough or surging idle, stalling, hesitation and, on electronic throttles, a reduced-power mode.
What a throttle body does
- Meters the air: the plate opening sets airflow, and the engine computer adds fuel to match.
- Reports its position: throttle position sensors tell the computer how far the plate is open.
- Controls idle: on electronic throttles the computer holds idle speed with the plate itself; older engines used a separate idle air control valve.
Cable vs electronic throttle
Older engines connect the pedal to the throttle plate with a cable, and a separate idle air control valve manages idle. Most modern engines use electronic throttle control: a pedal sensor reports what you ask for, and a motor in the throttle body opens the plate, which lets the computer smooth throttle response, hold idle and help traction and stability control. Electronic throttles have redundant sensors, and a disagreement between them is what triggers the reduced-power mode.
Bad throttle body symptoms
- Rough, high or surging idle, or stalling when coming to a stop
- Hesitation or poor response when pressing the pedal
- A reduced-power or limp mode with an electronic throttle fault
- Check engine light with throttle or pedal position codes
How to clean a throttle body
- With the engine off and cool, remove the intake duct from the throttle body.
- Spray throttle body cleaner onto a clean cloth or the carbon around the plate and bore, and wipe the deposits away.
- On electronic throttles, do not force the plate open by hand; follow the service manual, which may describe opening it with the key on.
- Refit the duct, start the engine and let it idle. Some vehicles need an idle relearn procedure afterward.
Carbon around the plate is a common cause of rough idle and stalling, so cleaning is often the first fix. If symptoms remain, the throttle position sensor or the electronic throttle motor may be at fault.
Throttle bodies and performance builds
Larger throttle bodies are a common upgrade on high-power engines, but they only help when the rest of the intake can flow more air, and the engine computer must be calibrated for them. The Performance Design Carbon pTR intake manifold for the engines in 2020-2025 Corvettes, for example, has a 105mm forward-facing throttle body flange that accepts 90 to 105mm throttle bodies. See what does an intake manifold do? and what does a cold air intake do?
Related: vacuum leak · MAF sensor · engine misfire.
More guides: rough idle · throttle position sensor · idle air control valve · car hesitates when accelerating.
Trouble codes: P2135 Throttle Position Sensor Correlation · P2138 Pedal Position Sensor Correlation · P2101 Throttle Actuator Motor Range · P0121 Throttle Position Sensor Range · P0507 Idle RPM Higher Than Expected · P0506 Idle RPM Lower Than Expected · P0068 MAP/MAF Throttle Position Correlation · P2122 Pedal Position Sensor D Low · P2111 Throttle Actuator Stuck Open · P2112 Throttle Actuator Stuck Closed · P0642 Sensor Reference Voltage A Low · U0107 Lost Communication With Throttle Module · P2119 Throttle Body Range/Performance · P2176 Idle Position Not Learned · P0220 Throttle Position Sensor B Circuit · all OBD2 codes.
Shipping is a flat $80.00 per order to US addresses, with 15-day free returns. Questions? Ask a parts specialist.