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.



Check Powertrain System, if not already completed

Check Ignition System, 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 IC Module

Check Fuel System, looking 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
- Binding ISC Motor
- Sticking TP Switch
- TP Sensor/Idle Learn Not Complete


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 VSS Readings
- Erratic Engine RPM Readings


Check PCV System.


Check EGR System.


Check EVAP Components.