1. Basic Checks (Easy and Cheap):
* Battery Voltage: A weak battery can cause erratic cold starts. Test the battery voltage with a multimeter. It should be above 12.6V when fully charged. Low voltage can affect the fuel pump, ignition system, and computer, all crucial for a smooth cold start.
* Fuel: Ensure you have fresh, clean fuel. Old, contaminated fuel can cause poor combustion.
* Air Filter: A clogged air filter restricts airflow, leading to a rough idle. Replace it with a new one.
* Vacuum Leaks: Inspect all vacuum hoses for cracks, holes, or loose connections. Even a small leak can disrupt the air/fuel mixture, especially important during cold starts. Pay close attention to hoses connected to the EGR valve, throttle body, and vacuum advance on the distributor. Use a vacuum gauge to check for leaks if you suspect a problem.
* Ignition System: Check the spark plug wires for cracks or wear. Worn distributor cap and rotor can also cause misfires. Inspect the ignition coil for cracks or damage. Weak spark plugs can struggle to ignite the fuel, especially when cold. Consider replacing these parts, as they are age-sensitive.
2. Cold Start Components (More Involved):
* Throttle Position Sensor (TPS): A faulty TPS provides incorrect information to the engine computer about the throttle position, affecting the cold-start fuel mixture. Test the TPS with a multimeter according to its specifications (you'll need a service manual or online resource specific to your Riviera's engine).
* Air Flow Meter (AFM) or Mass Air Flow Sensor (MAF): (Depending on engine type) The AFM/MAF measures the amount of air entering the engine. A dirty or faulty AFM/MAF can cause incorrect fuel delivery. Clean the AFM (if it's an AFM) with MAF sensor cleaner following the instructions carefully; replacement may be necessary if cleaning doesn't solve the problem.
* Cold Start Injector (CSI) or Cold Enrichment System: This system adds extra fuel during cold starts. It might be a dedicated injector or part of the fuel injection system's programming. A malfunctioning CSI or faulty wiring could be the culprit. This often requires testing the injector's operation and checking its wiring and connections. A service manual will be essential.
* Thermo-Time Switch (TTS): This switch controls the choke (if your Riviera has a choke system) or other cold-start functions based on engine temperature. A failing TTS might not provide the proper signal to activate the cold-start enrichment.
3. Engine Management System (Advanced):
* Engine Control Unit (ECU): While less likely, a faulty ECU could be the cause. This is the most expensive and challenging component to diagnose and replace. This requires specialized diagnostic equipment and expertise.
Troubleshooting Steps:
1. Start with the easy checks: Battery, fuel, air filter, vacuum leaks. These are the most common and least expensive to address.
2. Consult a repair manual: A factory service manual specific to your 1986 Buick Riviera will provide detailed diagnostic procedures and wiring diagrams. This is crucial for correctly testing components and avoiding damage.
3. Use a multimeter: To test the electrical components accurately, you'll need a multimeter.
4. Systematic approach: Address one potential problem at a time, testing and verifying before moving to the next.
5. Professional Help: If you're not comfortable working on your car's fuel injection system or ignition system, consult a qualified mechanic. Improper diagnosis or repair can cause further damage.
Remember that a 1986 Buick Riviera has a relatively complex fuel injection system. Trying to fix it without the proper knowledge and tools can be frustrating and potentially damaging. A service manual is highly recommended, and if you lack experience, seeking professional assistance is wise.
