Rough, Unstable, or Incorrect Idle, Stalling

DEFINITION
Engine runs unevenly at idle. If severe, the engine or vehicle may shake. Engine idle speed may vary in rpm. Either condition may be severe enough to stall engine.

PRELIMINARY INSPECTION
^ Perform the careful "Visual And Physical Checks" in Preliminary Checks. Testing and Inspection
^ CHECK: For vacuum leaks.
^ CHECK: PCM grounds for being clean, tight and proper routing. Refer to PCM wiring diagrams.

FUEL SYSTEM

Notice: Monitoring Oxygen Sensor (O2S) voltage will help identify the cause of the problem.
Lean - Refer to "Diagnostic Aids" under Diagnostic Trouble Code 25. DTC 25
Rich - Refer to "Diagnostic Aids" under Diagnostic Trouble Code 26. DTC 26

^ CHECK: Incorrect minimum idle speed may be caused by foreign material accumulation in the throttle bore, coking on the throttle valve or on the throttle shaft.
^ CHECK: Clean injectors.
^ CHECK: Fuel injector spray balance.
^ CHECK: For fuel in pressure regulator vacuum hose. If fuel is present, replace regulator assembly.
^ CHECK: EVAP Thermal Vacuum Valve (TVV) operation. Testing and Inspection
^ CHECK: The 02S should respond quickly to different throttle positions. If it does not, check the 02S for silicone 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 PCM will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem.

IGNITION SYSTEM
^ CHECK: Ignition timing. Refer to Ignition Timing Adjustment. Ignition Timing
^ CHECK: Ignition system; wires, plugs. rotor, etc.

ENGINE MECHANICAL
^ CHECK: Perform a cylinder compression check.
^ CHECK: For camshaft wear or weak valve springs.

ADDITIONAL CHECKS
^ CHECK: Manifold Absolute Pressure (MAP) sensor. Refer to DTC 31 MAP Sensor Circuit. Powertrain Controls - ECM/PCM
^ CHECK: Throttle linkage for sticking or binding.
^ CHECK: Idle Air Control (IAC) valve operation.
^ CHECK: A/C signal to PCM. If problem exists with A/C ON check A/C idle system operation. For additional information, refer to A/C Signal. A/C Signal
^ CHECK: For PCM calibration updates, refer to PROM. PROM - Programmable Read Only Memory
^ CHECK: For broken motor mounts.
^ CHECK: Generator output voltage. Repair if less than 12 or more than 16 volts.
^ CHECK: Electrical load idle-up circuit. Refer to Voltage Signal. Voltage Signal
^ CHECK: PCV valve for proper operation. Refer to PCV Valve Functional Test. Testing and Inspection
^ CHECK: EGR valve. There should be no EGR at idle (If equipped). Refer to Exhaust Gas Recirculation System Check. Testing and Inspection