Rough/Unstable Idle or Stalls

SYMPTOM DESCRIPTION:


The engine runs unevenly at idle. If bad enough, the vehicle may shake. Also, the idle may vary in rpm (called "hunting"). Either condition may be severe enough to cause stalling. Engine idles at incorrect speed.


POSSIBLE CAUSE ACTION


CHARGING SYSTEM MALFUNCTION Check Battery voltage.

Check Alternator output voltage.




IGNITION SYSTEM MALFUNCTION Scope check Ignition System

Check IGNITION COIL for proper output voltage.

Check SPARK PLUGS for proper spark duration. Remove spark plugs, check for fuel fouled plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits. Replace as necessary.

Check SECONDARY CIRCUIT for abnormal firing Kv, crossfire between spark plugs (distributor cap, spark plug wires), and proper plug wire routing.

Check IGNITION TIMING for excessive spark retard.



ENGINE MECHANICAL MALFUNCTION Check COMPRESSION Perform a compression check, and cylinder leakage test, look for weak cylinders.

Check for VACUUM LEAKS inspect Intake manifold, gasket(s), and hoses.

Check exhaust system for leaks, restriction, or damage.

Check for incorrect valve timing.



EMISSIONS COMPONENT MALFUNCTION Check EGR valve for binding or sticking in the open position.

Check EGR Transducer for proper operation.

Check Evaporative control system.

Check for plugged or contaminated Catalytic Converter.



FUEL SYSTEM MALFUNCTION Check for incorrect Air-Fuel mixture, O2 Sensor, perform injector balance test, inspect regulator operation (check vacuum line and return hose), check fuel pressure.

Check plugged or restricted Fuel Filter.

Check plugged or restricted Air Filter.

Check fuel quality.