1. Safety First:
* Disconnect the negative battery terminal. This prevents accidental shorts and damage to your vehicle's electronics.
2. Access the Throttle Body:
* Locate the throttle body. It's usually on the intake manifold, connected to the air intake. You'll likely need to remove some air intake components to access it properly. Consult your vehicle's repair manual for precise location and removal instructions.
3. Inspection:
* Visual Inspection: Carefully inspect the throttle plate (the butterfly valve) and its shaft. Look for:
* Debris: Dirt, carbon buildup, or other debris can jam the throttle plate.
* Damage: Bent or damaged throttle plate or shaft.
* Corrosion: Rust or corrosion on the shaft or inside the throttle body bore.
* Worn bushings: The shaft may have worn bushings, causing it to bind.
* Manual Operation: With the throttle cable disconnected (carefully!), try manually moving the throttle plate. It should move freely and smoothly. If it sticks, you've identified the problem area.
4. Cleaning:
* Thorough Cleaning: If you find debris or carbon buildup, clean the throttle body thoroughly. Use throttle body cleaner (available at auto parts stores) and follow the instructions on the can. Pay close attention to the throttle plate, shaft, and bore. Use a clean rag or shop towels to wipe away the residue. Avoid spraying cleaner directly onto the TPS if possible.
5. Addressing Mechanical Issues:
* Bent Plate or Shaft: If the throttle plate or shaft is bent, it will likely need replacement. This usually requires a new throttle body.
* Worn Bushings: If the bushings are worn, replacing the entire throttle body is generally the most practical solution, especially considering the age of your vehicle. Individual bushings are sometimes available, but replacement is more challenging.
* Corrosion: Try to remove any corrosion using a wire brush or a specialized cleaning tool. If the corrosion is significant, replacement might be necessary.
6. TPS (Throttle Position Sensor):
* While the sticking issue *sounds* mechanical, a faulty TPS can sometimes cause symptoms that mimic a sticking throttle body, especially around idle. After cleaning the throttle body, if the problem persists:
* Inspect the TPS: Look for damage or loose connections.
* Test the TPS: You might need a multimeter to check the TPS voltage output to ensure it's within specifications. Consult your repair manual or online resources for the correct procedure. A faulty TPS needs replacement.
7. Reassembly and Testing:
* After cleaning or replacing parts, carefully reassemble everything.
* Reconnect the battery.
* Start the engine and test for smooth operation. Pay close attention to throttle response, especially coming off idle.
Important Notes:
* Repair Manual: A repair manual specific to your 1999 GMC Safari is invaluable. It will provide detailed diagrams, torque specifications, and troubleshooting information.
* Throttle Cable: While less likely to cause the issue you describe, inspect and lubricate your throttle cable if you're having persistent problems.
* Replacement Throttle Body: If cleaning and addressing mechanical issues doesn't resolve the problem, replacing the throttle body is often the most effective solution. Ensure you get a replacement throttle body specifically for your 4.3L V6 engine.
If you're uncomfortable performing this repair yourself, it's best to take your vehicle to a qualified mechanic. A misdiagnosed or improperly repaired throttle body can lead to more serious engine problems.
