Rough, Unstable, or Incorrect Idle, Stalling

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

POWERTRAIN SYSTEM
Perform Powertrain System Check, if not already completed. Chart 1 Powertrain System Check

IGNITION SYSTEM
Perform Chart 6D4-1 Ignition System Check, looking in particular for:

^ High Resistance, Open, Shorted, or Arcing Spark Plug Wires, crossfire between spark plug wires
^ Contaminated or Damaged Spark Plugs
^ Faulty Coil Pack or Ignition Control (IC) Module

Chart 1 Ignition System Check

FUEL SYSTEM
Perform Chart 6C-1 Fuel System Check looking in particular for:

^ Fuel Quality
- Alcohol Content
- Contaminants
- Water Content
- Sour Fuel
^ Low Fuel Pressure
^ Fuel Injectors
- Not Operating
- Low Flow Rate

Chart 6C-1 Fuel System Check

AIR INDUCTION
^ Idle Speed Control
- Binding ISC Motor
- Sticking TP Switch
- TP Sensor/Idle Learn Not Complete

^ Incorrect minimum idle speed may be caused by foreign material accumulation in the throttle bore, coking on the throttle valve or shaft, and throttle body tampering.

MECHANICAL CAUSES
Check for the following mechanical causes:
- Intake Valve Deposits
- Valves Sticking in Guides
- Vacuum Leaks in Intake Manifold System
- Broken/Weak Valve Springs
- Collapsed Lifter
- Camshaft Timing
- Low Engine Compression
- Binding or Sticking Throttle and/or Cruise Cables
- Erratic A/C Compressor Clutch operation
- Erratic Vehicle Speed Sensor (VSS) Readings
- Erratic Engine rpm Readings

POSITIVE CRANKCASE VENTILATION SYSTEM
Perform PCV System Check. Positive Crankcase Ventilation

EXHAUST GAS RECIRCULATION
Check EGR System. Refer to Chart 6EC-1 EGR System Check. Chart 6EC-1 EGR System Check

EVAPORATIVE EMISSIONS (EVAP)
Perform functional tests of EVAP components. Evaporative Emissions System