Stalls/Rough, Unstable or Incorrect Idle

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.




SYSTEM OR COMPONENT TO CHECK ACTION

COMPUTER INPUTS/OUTPUTS CHECK: ^ ENGINE SPEED/REFERENCE SENSOR:
Check for improperly positioned or damaged sensor.
^ IDLE VALVE:
^ AIR FLOW METER:
^ OXYGEN SENSOR (O2) - Inspect sensor for
silicon contamination from fuel, or use of
improper RTV sealant. The sensor will have
a white, powdery coating, and will result
in a high but false signal voltage (rich
exhaust indication). The electronic control unit will
then reduce the amount of fuel delivered to the
engine, causing a severe driveability
problem.
^ THROTTLE SWITCH: Improper adjustment
^ COOLANT TEMPERATURE SENSOR:







FUEL

^ FUEL INJECTOR BALANCE TEST: Poor spray
pattern, clogged or stuck
^ FUEL PRESSURE: Check fuel pressure
and output volume.




IGNITION CHECK: ^ SECONDARY IGNITION SYSTEM:
^ ELECTRONIC CONTROL UNIT: Final output stages.



EMISSIONS CHECK: ^ EVAPORATIVE SYSTEM:
Test purge valve and charcoal canister operation.
^ PCV VALVE: Test for proper operation.
NOTE: ^ Refer to EMISSION CONTROLS
for complete testing procedures.




ENGINE CHECK: ^ VACUUM LEAKS: Test for vacuum leaks
at intake system.
^ BATTERY: Cables and ground straps should be
clean and secure.
^ CRANKCASE AIR LEAKS: Check at dip stick seal,
oil filler cap, front and rear engine oil seals.
^ A/C refrigerant pressure too high,
overcharge or faulty high pressure switch.
^ MOTOR MOUNTS:
^ CYLINDER COMPRESSION: