Throttle body
Throttle body refers to the air-control assembly used by the Pontiac Fiero engine.
The throttle body controls the amount of air entering the engine. It also carries or works with several important engine-management parts, including the Throttle position sensor and Idle air control valve.
Overview
The throttle body is part of the intake system.
When the accelerator pedal is pressed, the throttle linkage opens the throttle plate. This allows more air into the engine. The ECM then uses sensor information to adjust fuel delivery and other engine-control functions.
On fuel-injected Fieros, the throttle body is closely connected to idle control, throttle response, drivability, and diagnostic trouble codes.
Location
Image wanted: Photo or diagram showing the throttle body location. Ideally include both the 2.8L V6 throttle body and the 2.5L four-cylinder throttle body.
The throttle body is mounted on the intake side of the engine.
On the 2.8L V6, the throttle body is mounted on the upper intake plenum.
On the 2.5L four-cylinder, the throttle body is part of the throttle body injection assembly.
The exact appearance and access differ between the 2.8L V6 and 2.5L four-cylinder engines.
Main parts
Throttle-body-related parts may include:
- Throttle plate
- Throttle shaft
- Throttle linkage
- Throttle position sensor
- Idle air control valve
- Idle air passages
- Vacuum ports
- Throttle body gasket
- Fuel injector assembly on throttle-body-injected engines
Throttle position sensor
The Throttle position sensor is mounted on the throttle body and reports throttle opening to the ECM.
Related trouble codes include:
- Code 21 - Throttle position sensor circuit, high voltage
- Code 22 - Throttle position sensor circuit, low voltage
Idle air control valve
The Idle air control valve is mounted on the throttle body and allows the ECM to control idle air flow.
A dirty throttle body, blocked idle passage, faulty IAC valve, vacuum leak, or throttle linkage problem can cause idle-control problems.
Related trouble codes include:
- Code 35 - Idle speed error
Common problems
Common throttle-body-related problems include:
- Dirty throttle plate
- Carbon buildup
- Sticking throttle plate
- Sticking throttle linkage
- Vacuum leaks
- Bad throttle body gasket
- Dirty idle air passages
- Faulty or misadjusted TPS
- Faulty or sticking IAC valve
- Previous incorrect adjustment
Symptoms
Possible symptoms of throttle body, TPS, or IAC problems include:
- High idle
- Low idle
- Rough idle
- Surging idle
- Stalling
- Poor throttle response
- Hesitation
- Poor acceleration
- Check engine light
- Code 21
- Code 22
- Code 35
Diagnosis
Basic diagnostic checks include:
- Check for stored diagnostic trouble codes.
- Inspect throttle linkage movement.
- Check that the throttle plate returns fully.
- Inspect the throttle body for dirt or carbon buildup.
- Check for vacuum leaks.
- Inspect the Throttle position sensor connector and wiring.
- Inspect the Idle air control valve connector and wiring.
- Check TPS signal through ALDL diagnostics if live data is available.
- Check IAC behavior or IAC counts through ALDL if available.
- Check for previous incorrect adjustment.
Cleaning
Throttle body cleaning may help if the throttle plate or idle air passages are dirty.
General cautions:
- Use products safe for throttle bodies and sensors.
- Avoid forcing the throttle plate or damaging the shaft.
- Avoid spraying excessive cleaner into electrical parts.
- Do not damage gaskets or vacuum lines.
- Do not adjust stop screws unless following the correct service procedure.
Idle adjustment caution
Do not randomly adjust throttle stop screws or minimum-air settings to correct idle problems.
High idle or unstable idle is often caused by vacuum leaks, IAC problems, dirty passages, TPS problems, EGR leaks, or wiring faults. Incorrect adjustment can mask the real problem and make later diagnosis harder.
Relationship to vacuum leaks
A vacuum leak near the throttle body can cause high idle, lean running, hesitation, or idle-control problems.
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