1. Determine if it's Carbureted or Fuel Injected:
* Carbureted: Older 1992 models might have a carburetor. Look under the hood; a carburetor is a large, usually metallic, unit on top of the engine.
* Fuel Injected: Most 1992 vehicles with a 350 would be fuel-injected. You'll see various sensors and fuel rails instead of a carburetor.
2. Adjusting Idle Speed (Carbureted):
This is more hands-on and requires a screwdriver. Caution: Improper adjustment can lead to poor engine performance.
* Locate the Idle Speed Screw: It's usually on the side of the carburetor. It's a small screw with a slot for a screwdriver.
* Warm Up the Engine: Let the engine run until it reaches normal operating temperature.
* Adjust Slowly: Turn the idle speed screw slightly. A small adjustment can make a noticeable difference. Turn it clockwise to increase idle speed and counterclockwise to decrease it.
* Monitor the RPM: Use a tachometer (highly recommended) or listen to the engine to gauge the idle speed. Consult your owner's manual for the recommended idle speed (usually around 650-850 RPM).
* Adjust and Test: Make small adjustments, letting the engine settle after each turn. Continue until you reach the desired RPM.
3. Adjusting Idle Speed (Fuel Injected):
Fuel-injected systems are generally computer-controlled. Manual adjustment is limited and usually not recommended unless you're experienced with automotive diagnostics. An improper adjustment can trigger a check engine light or cause poor performance.
* Check for Trouble Codes: Use an OBD-I scanner (for a 1992 vehicle) to check for any diagnostic trouble codes (DTCs). This can indicate underlying problems affecting idle.
* Throttle Position Sensor (TPS): A faulty TPS can affect idle. A mechanic can test the TPS and replace it if necessary.
* IAC Valve (Idle Air Control Valve): The IAC valve controls idle speed electronically. A dirty or faulty IAC valve will affect idle. Cleaning or replacing the IAC may be necessary.
* Computer Calibration: There is no direct idle screw adjustment; the computer controls the idle speed. You might need a scanner to access and adjust idle settings (this is an advanced procedure and not recommended for DIYers).
* Professional Help: If you're not comfortable with these aspects, take your vehicle to a qualified mechanic for diagnosis and repair.
Before you begin any adjustments:
* Consult your owner's manual: It will provide specific idle speed recommendations and possibly adjustment procedures.
* Safety First: Work on a cool, well-ventilated area. Disconnect the negative battery terminal before working on the engine.
In summary, adjusting the idle speed on a fuel-injected 1992 350 is best left to a mechanic unless you're experienced with automotive diagnostics and repair. A carbureted system is easier to adjust manually, but still requires caution and a understanding of how the system works. A tachometer is highly recommended for any adjustment to precisely monitor RPM.
