1. Vacuum Leaks: This is the most common culprit after an engine swap. The vacuum system is crucial for idle control, and even a tiny leak can cause significant problems.
* Check: Visually inspect all vacuum lines for cracks, loose connections, or damage. Pay close attention to lines connected to the brake booster, PCV valve, and the throttle body. Use a vacuum gauge to check system integrity. A hissing sound near vacuum lines is a good indication of a leak.
2. Throttle Position Sensor (TPS): The TPS tells the computer the throttle's position. A faulty TPS can lead to erratic idle and stalling.
* Check: Test the TPS voltage output with a multimeter. The voltage should change smoothly as you move the throttle. A faulty TPS needs replacement.
3. Mass Airflow Sensor (MAF) Sensor: The MAF measures the amount of air entering the engine. A dirty or faulty MAF sensor can cause inaccurate fuel delivery, resulting in idle problems.
* Check: Carefully clean the MAF sensor with MAF sensor cleaner (follow the instructions carefully, avoid touching the sensor element). If cleaning doesn't solve it, the sensor might need replacement.
4. Idle Air Control (IAC) Valve: This valve regulates the air entering the engine at idle. A dirty or faulty IAC valve can lead to erratic idle.
* Check: Clean the IAC valve with carb cleaner or throttle body cleaner. If cleaning doesn't solve the problem, it may need to be replaced.
5. Computer/ECM Issues: If the engine wasn't properly programmed after the swap or there's a problem with the computer itself (unlikely but possible), it could lead to issues.
* Check: Have the engine's computer scanned for trouble codes using an OBD-I scanner (you'll need one specific to that year Caprice). This might reveal underlying issues.
6. Incorrect Engine Calibration/Tuning: The engine's calibration (fuel maps etc.) might not be suitable for the specific components installed. This is especially true for swapped engines.
* Check: If the engine is tuned via a programmable ECU, a proper tuning may be needed. This requires specialized knowledge and equipment.
7. Fuel Delivery Problems: Issues with the fuel pump, fuel filter, or fuel injectors can also lead to fluctuating idle and stalling.
* Check: Check fuel pressure with a gauge. Replace the fuel filter if it's old. Consider having the injectors cleaned or tested.
8. Wiring Issues: Double-check all wiring connections related to the engine and its sensors after the swap. A loose or damaged wire can interrupt signals and cause problems.
Troubleshooting Steps:
1. Start with the simplest: Begin by checking for vacuum leaks. They are the most frequent culprits.
2. Systematically check components: Proceed through the list above, testing each component and addressing any problems you find.
3. Professional Help: If you're not comfortable working on your car's electrical and fuel systems, take it to a mechanic experienced with GM vehicles and engine swaps. They have the tools and expertise to diagnose the problem more effectively.
Remember to document your findings and the steps you've taken. This will help you and the mechanic if you need further assistance. The key is systematic troubleshooting.
