Rough, Unstable, or Incorrect Idle, Stalling

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

POWERTRAIN SYSTEM CHECK
Perform Chart 1 Powertrain System Check. Chart 1 Powertrain System Check

IGNITION SYSTEM CHECK
Perform Chart C-1 Ignition Control Performance Test. Check in particular for:

^ High resistance, open, shorted, or arcing spark plug wires, crossfire between spark plug wires
^ Contaminated or damaged spark plugs
^ Distributor grounding points clean and tight
^ Correct ignition timing
^ Faulty ignition coil or Ignition Control (IC) module
^ Distributor cap, rotor, brush and button for moisture, cracks, dust or carbon tracking
^ Worn or loose distributor shaft gear
^ Bent distributor shaft or worn distributor shaft bushing

C Charts

FUEL SYSTEM CHECK
Perform Chart 6C-1 Fuel System Check. Check in particular for:
^ Fuel Quality
- alcohol content
- contaminants
- water content
- sour fuel
^ Low Fuel Pressure
^ Fuel injectors
- not operating
- low flow rate
^ Idle speed control (ISC)
- binding ISC motor
- sticking Throttle Position (TP) switch
- Throttle Position sensor/Idle learn not complete

Chart 6C-1 Fuel System Check

MECHANICAL CAUSES
Check for the following mechanical causes:

^ Throttle body deposits
^ Intake valve deposits
^ Valves sticking in guides
^ Vacuum leaks in intake manifold
^ Loose timing chain (timing gear wear)
^ Broken or weak valve springs
^ Collapsed lifter
^ Bent push rods
^ Worn camshaft lobes
^ Worn rocker arms
^ Low engine compression
^ Binding or sticking throttle or throttle valve and/or cruise control cables
^ Erratic A/C compressor clutch operation
^ Erratic Vehicle Speed Sensor (VSS) readings
^ Erratic engine RPM readings

PCV SYSTEM
Perform Positive Crankcase Ventilation (PCV) system check.

EXHAUST GAS RECIRCULATION (EGR) SYSTEM CHECK
Perform Chart 6EC-2 EGR System Check. Chart 6EC-2 EGR System Check

EVAPORATIVE EMISSIONS (EVAP) SYSTEM CHECK
Perform Chart 6EC-1 EVAP System Check. Chart 6EC-1 EVAP System Check