1. Fuel Delivery:
* Fuel Filter: A clogged fuel filter restricts fuel flow, leading to poor idle and stalling under load (like when shifting into gear). This is a cheap and easy part to replace first.
* Fuel Pump: A weak fuel pump might deliver enough fuel at idle but struggle when the engine demands more power in gear. Listen for a whining sound from the fuel pump (usually near the fuel tank) – a weak pump often sounds louder or different than a healthy one. Fuel pressure testing is the definitive way to diagnose a pump problem.
* Fuel Injectors: Clogged or failing injectors can cause inconsistent fuel delivery, leading to rough idling and stalling. This is a more involved diagnostic process often requiring specialized tools.
2. Ignition System:
* Distributor Cap and Rotor: Worn or cracked distributor caps and rotors can cause misfires, leading to poor idling and stalling. Inspect them visually for cracks, carbon tracking, or corrosion.
* Ignition Coil: A weak ignition coil can't provide enough spark to ignite the fuel-air mixture consistently.
* Spark Plugs and Wires: Worn or fouled spark plugs and damaged wires lead to misfires. Check for gap and wear on plugs; inspect wires for cracks or damage.
3. Vacuum Leaks:
* Vacuum Hoses: Cracked, disconnected, or deteriorated vacuum hoses disrupt the engine's control systems. Inspect all vacuum lines carefully, paying close attention to those connected to the brake booster, PCV valve, and other components. Even a small leak can cause significant problems.
4. Transmission Issues (Less Likely, but Possible):
While the stalling *seems* directly related to putting it in gear, it could be a symptom of a transmission problem putting extra load on the engine, revealing a weak engine that would otherwise idle okay. However, this is less likely given the poor idle as well.
5. Other Potential Issues:
* Throttle Position Sensor (TPS): This sensor tells the computer the throttle position, and a faulty one can cause idle problems and stalling.
* Idle Air Control (IAC) Valve: This valve regulates airflow at idle. A dirty or faulty IAC valve can result in a rough idle and stalling.
* Mass Air Flow (MAF) Sensor: Measures the amount of air entering the engine. A dirty or faulty MAF sensor can lead to poor running.
* Computer/ECM Problems: Though less common, a failing Engine Control Module (ECM) could be the root cause. This is usually diagnosed last.
Troubleshooting Steps:
1. Start with the easy checks: Fuel filter, visual inspection of vacuum hoses, distributor cap and rotor, spark plugs and wires.
2. Listen for unusual noises: Whining from the fuel pump, ticking from the injectors, etc.
3. Check engine codes (if equipped): A code reader can pinpoint potential problems. Many auto parts stores will scan your codes for free.
4. Consider professional help: If you're not comfortable diagnosing these issues yourself, take it to a mechanic specializing in older vehicles. They have the experience and tools to diagnose the problem efficiently.
Remember to be safe when working on your car. Disconnect the negative battery terminal before starting any work on the electrical system.
