Rough/Unstable Idle or Stalling

Definition: The engine runs unevenly at idle. If bad enough, the vehicle may shake. Also, the idle may vary in rpm. Either condition may be severe enough to cause stalling. Engine idles at incorrect speed.
POSSIBLE CAUSE ACTION
Restricted air cleaner Replace air cleaner element

curb or fast idle speed misadjusted Perform idle adjustment. Curb Idle Speed Adjustment

Vacuum hose/carburetor/manifold leak Inspect and repair vacuum leaks, retorque manifold and carburetor base, check carburetor air horn screws.

Carburetor idle passages/adjusting needles dirty Clean idle passages, replace adjusting needles. Carburetor Overhaul/Replacement

Throttle valves sticking/worn throttle shaft Lubricate throttle valves, replace worn throttle valve shaft. Carburetor Overhaul/Replacement

Float leaking or misadjusted Replace leaking needle and seat. Carburetor Overhaul/Replacement
Perform float level adjustment.

Choke not opening Check operation and repair, replace or adjust as needed. Choke Adjustments

Restricted exhaust system Test exhaust system.

EGR valve stuck open Check EGR valve and repair or replace as needed.

Clogged EGR nipple or passage Check EGR and repair or replace as needed.

Clogged primary pilot jet Check operation and repair or replace as needed.

Malfunctioning dashpot Check operation and repair or replace as needed.

Malfunctioning slow cut solenoid valve Check operation and repair or replace as needed.

Malfunctioning slow cut solenoid valve Check operation and repair or replace as needed.

Malfunctioning engine coolant temperature sensor Check operation and repair or replace as needed.

Malfunctioning throttle position sensor Check operation and repair or replace as needed.

Malfunctioning engine speed sensor Check operation and repair or replace as needed.

Malfunctioning timing control system Check operation and repair or replace as needed.

Malfunctioning throttle opener control system Check operation and repair or replace as needed.

Broken, short circuited or incorrectly
connected harness connector Check wiring and connectors and repair or replace as needed.