Here are several potential culprits:
* Fuel Delivery: A clogged fuel filter, a failing fuel pump (weak pressure), or issues within the fuel injectors (clogged or malfunctioning) could all restrict fuel flow, leading to a lack of power and potential stalling, even in neutral. The fuel pressure should be checked.
* Ignition System: Problems in the ignition system (spark plugs, wires, distributor cap and rotor, ignition coil, ignition control module (ICM)) can cause misfires, hesitation, and stalling. Worn or fouled spark plugs are a common cause of this type of issue. Check for spark at the plugs and visually inspect all components for wear or damage.
* Mass Airflow Sensor (MAF) or Throttle Position Sensor (TPS): These sensors tell the engine's computer how much air is entering and the throttle position. A faulty sensor can send incorrect information, leading to a lean fuel mixture (too much air, not enough fuel), resulting in poor performance and potential stalling.
* Vacuum Leaks: Vacuum leaks in the intake system can disrupt the proper air/fuel mixture, causing similar symptoms. Inspect all vacuum lines and connections for cracks or damage.
* Engine Computer (ECM): While less likely, a faulty engine control module could be causing the problem. This is harder to diagnose and often requires professional testing.
* Catalytic Converter: A severely clogged catalytic converter can restrict exhaust flow, leading to backpressure that affects the engine's ability to breathe and produce power. This would be more pronounced under load (in gear), but a severely clogged converter could still cause issues even in neutral.
Troubleshooting Steps:
1. Check the basics: Start with the easiest things to check:
* Fuel: Check the fuel level. A nearly empty tank can sometimes cause issues.
* Battery: Make sure the battery is properly charged. A weak battery can affect the ignition system.
* Spark Plugs and Wires: Inspect for wear, fouling, or damage. Replace if necessary.
2. Listen for unusual noises: Does the engine make any unusual noises (knocking, ticking, whining) while running?
3. Get a diagnostic code scan: Use an OBD-II scanner (some auto parts stores will scan for free) to see if any trouble codes are stored in the engine computer. This can give you a good starting point for diagnosis. Note that 1989 vehicles may not fully support OBD-II, so a scanner specifically for older GM vehicles might be needed.
4. Professional Help: If you are not comfortable working on your car yourself, take it to a qualified mechanic for diagnosis and repair. They have the tools and expertise to properly diagnose the problem.
Since the problem occurs in neutral, focus your attention on the fuel system, ignition system, and sensors first. A vacuum leak is also a strong possibility. The catalytic converter is less likely to be the primary cause, but should be considered if other checks prove inconclusive.
