First, determine your fuel system:
* Carburetor: Look under the hood. If you see a large, cylindrical device with a lot of linkages and vacuum lines, you have a carburetor.
* Throttle Body Injection (TBI): This system looks more like a mini-fuel injection system integrated into the throttle body. It's a less complex system than a full fuel injection system.
Adjusting the Idle (Carburetor System):
If you have a carburetor:
1. Warm up the engine: Let the engine run until it reaches normal operating temperature.
2. Locate the idle adjustment screw: This is usually a small screw on the carburetor, often accessible from the top. It's often labeled or near a linkage. Consult your owner's manual or a repair manual specific to your engine (e.g., 22R, 20R) for the precise location.
3. Adjust slowly: Turn the screw slightly (1/8 to 1/4 turn at a time). Turning it clockwise will generally increase the idle speed, and counter-clockwise will decrease it.
4. Check the RPM: Monitor the engine speed using a tachometer (ideal) or by listening for changes. Your owner's manual will specify the correct idle speed (usually around 750-850 RPM).
5. Repeat: Continue adjusting the screw until the idle speed is correct.
6. Fast Idle Cam: Some carburetors have a fast idle cam to raise the idle speed when the engine is cold. Make sure this is working correctly.
7. Air/Fuel Mixture: If the idle is too high or low, even after adjusting the idle speed screw, the air/fuel mixture might need adjustment. This is more complex and requires more specialized tools and knowledge.
Adjusting the Idle (Throttle Body Injection System):
If you have TBI:
The idle adjustment on a TBI system is usually less accessible and involves the computer. Direct adjustment isn't typically recommended for this system. Instead:
1. Diagnosis is Key: An improper idle on a TBI system usually indicates an underlying problem. Before attempting anything, check for:
* Vacuum Leaks: Inspect all vacuum hoses for cracks or loose connections.
* Throttle Position Sensor (TPS): A faulty TPS can cause idle issues. This sensor needs testing with a multimeter.
* Air Flow Meter (AFM) or Mass Air Flow Sensor (MAF): A dirty or faulty AFM/MAF can also cause idle problems. Cleaning or replacing might be necessary.
* Idle Air Control (IAC) Valve: This valve regulates air flow at idle. It might need cleaning or replacement.
2. Professional Help: Given the computer-controlled nature of TBI, attempting adjustments without proper diagnostic tools and knowledge is risky. It's highly recommended to take your vehicle to a mechanic familiar with this system. Improper adjustment can damage components or lead to poor engine performance.
Important Considerations:
* Owner's Manual: Your owner's manual is the best source of information specific to your truck.
* Repair Manual: A repair manual (Haynes or Chilton) will provide detailed instructions and diagrams.
* Safety First: Always disconnect the negative battery terminal before working on the engine.
* Professional Mechanic: If you're uncomfortable working on your vehicle's fuel system, it's always best to take it to a qualified mechanic.
This information is for guidance only. Improper adjustments can damage your engine. Proceed with caution and consult a repair manual for detailed instructions specific to your 1986 Toyota pickup's engine.
