1. Idle Air Control (IAC) Valve: This is the most likely suspect. The IAC controls the airflow at idle, allowing the engine to run smoothly when cold and warm. A dirty or malfunctioning IAC valve can cause a rough idle, especially when cold, because the engine struggles to get the correct air/fuel mixture.
* Troubleshooting: Try cleaning the IAC valve with a throttle body cleaner. This often resolves the issue. If cleaning doesn't work, replacement might be necessary. (Disconnect the battery negative terminal before working on electrical components.)
2. Mass Airflow Sensor (MAF) Sensor: The MAF sensor measures the amount of air entering the engine. A dirty or failing MAF sensor will provide inaccurate readings, leading to a poor air/fuel mixture, particularly noticeable at idle and during cold starts.
* Troubleshooting: Inspect the MAF sensor for dirt or debris. Clean it carefully with MAF sensor cleaner (never use anything else!). If cleaning doesn't resolve the issue, the sensor might need replacement.
3. Throttle Position Sensor (TPS): The TPS tells the computer the throttle position. An inaccurate signal can cause poor idle and cold start issues.
* Troubleshooting: This often requires a scan tool to check the TPS voltage readings to see if it's within spec. Replacement is common if it's faulty.
4. Fuel Pressure Regulator: A faulty fuel pressure regulator could cause inconsistent fuel pressure, leading to rough idle and cold start difficulties.
* Troubleshooting: Requires a fuel pressure gauge to check fuel pressure at idle and while revving the engine. Low or inconsistent pressure points to a faulty regulator.
5. Coolant Temperature Sensor (CTS): This sensor tells the computer the engine's temperature. An inaccurate reading can cause the computer to use incorrect fuel mixtures, especially during cold starts.
* Troubleshooting: A faulty CTS can be tested with a multimeter. Its resistance changes with temperature. Replace if the readings are incorrect.
6. Ignition System Components: While less likely given the good running condition once warm, weak spark plugs, wires, or distributor cap/rotor could contribute to a rough idle and hesitant cold start.
* Troubleshooting: Check the spark plugs and wires for wear or damage. Replace if necessary. Inspect the distributor cap and rotor for cracks or arcing.
7. Vacuum Leaks: Small vacuum leaks can disrupt the air/fuel mixture, particularly noticeable at idle.
* Troubleshooting: Visually inspect all vacuum hoses for cracks or loose connections. Use a vacuum gauge to check for leaks if you suspect this is a problem.
Troubleshooting Steps:
1. Start with the easiest and cheapest: Clean the IAC valve and MAF sensor.
2. Use a scan tool: A OBD-I scanner (for your 1992 Corvette) will retrieve diagnostic trouble codes (DTCs) that can pinpoint the problem. This is invaluable.
3. Check fuel pressure: If the problem persists, check fuel pressure.
4. Systematically test components: Work your way through the other components (TPS, CTS, ignition system) based on your findings.
Important Note: A mechanic familiar with the LT1 engine can diagnose the problem much faster and more accurately. If you're uncomfortable tackling this yourself, take it to a qualified technician. Ignoring the issue could lead to further damage.
