1. Fuel Delivery Issues (Even if it starts):
* Fuel Pressure: This is crucial. You need a fuel pressure gauge to accurately measure pressure. The pressure should be within the manufacturer's specifications (check your repair manual). Low pressure could indicate a weak fuel pump, clogged fuel filter, or problems in the fuel lines. The pressure should remain consistent even while the engine is running. A pressure *drop* when the engine runs suggests a problem with the pump, regulator, or a leak.
* Fuel Pump Relay: A faulty relay might be preventing the pump from receiving power consistently. Try swapping the fuel pump relay with another (like the horn relay – be careful to note which is which).
* Clogged Injector(s): While less likely to cause a stall after a short run, a clogged injector could starve the engine of fuel after a short period. Consider a fuel injector cleaner additive (follow instructions carefully) or professional injector cleaning/testing.
2. Ignition System Problems (Beyond Timing):
* IAC (Idle Air Control) Valve: This is a very common cause of this problem. The IAC valve controls the air bypassing the throttle plate at idle. A dirty, sticking, or faulty IAC valve will prevent the engine from maintaining a consistent idle. Clean it thoroughly with carburetor cleaner (paying attention to the internal passageways) or replace it.
* MAP (Manifold Absolute Pressure) Sensor: This sensor tells the computer how much air is entering the engine. A bad MAP sensor can cause erratic idle and stalling. Testing this typically requires a multimeter and comparison to factory specifications (check a repair manual).
* Throttle Position Sensor (TPS): A faulty TPS might be giving incorrect signals to the computer, leading to poor idle control. This should be tested with a multimeter as well.
* Distributor Cap and Rotor: Even with correct timing, worn or damaged components in the distributor can cause intermittent spark, leading to stalling. Inspect for cracks, carbon tracking, or corrosion.
* PCV Valve: A clogged Positive Crankcase Ventilation valve can cause excessive crankcase pressure, affecting idle and potentially stalling the engine. A simple test is to remove it and check for free airflow.
3. Vacuum Leaks:
* A significant vacuum leak can prevent the engine from maintaining a steady idle. Check all vacuum lines for cracks, leaks, or loose connections. Use a vacuum gauge to check for vacuum leaks; a significant drop indicates a problem.
Troubleshooting Steps:
1. Start with the easy checks: Fuel filter, PCV valve, visual inspection of vacuum lines and the distributor cap/rotor.
2. Use a fuel pressure gauge: This is the most important step to rule out fuel delivery problems.
3. Check the IAC valve: This is a high-probability cause based on your description. Clean or replace it.
4. Use a multimeter: Test the MAP sensor and TPS.
5. If all else fails: Consult a repair manual specific to your 1989 Chevy S10 4.3L. The manual will provide detailed diagnostic procedures and specifications for testing various components.
Remember safety precautions when working with automotive systems, particularly around fuel and electrical components. If you're not comfortable performing these checks yourself, take it to a qualified mechanic. The cost of diagnosis is far less than replacing parts unnecessarily.
