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 CHECKS
^ Perform the careful visual/physical checks as described at start of "Symptoms".
^ CHECK: For vacuum leaks.
^ CHECK: PCM grounds for being clean, tight and proper routing. Refer to PCM wiring diagrams.

ADDITIONAL CHECKS
^ CHECK: MAP sensor. Refer to CHART C-1D.Chart C-1D Manifold Absolute Pressure (MAP) Output Check
^ CHECK: Throttle linkage for sticking or binding.
^ CHECK: Transaxle range switch circuit. Use Tech 1 scan tool and be sure tool indicates gear range selected.
^ CHECK: IAC valve operation, use CHART C-2BChart C-2B Idle Air Control (IAC) System Check.
^ CHECK: EGR valve. There should be no EGR at idle. Refer to CHART C-7Chart C-7 EGR System Check.
^ CHECK: A/C request signal to PCM, Tech 1 scan tool should indicate A/C is being requested whenever A/C is selected. If problem exists with A/C "ON," check A/C system operation, use CHART C-10Chart C-10 A/C Clutch Control Circuit Diagnosis.
^ CHECK: Crankcase ventilation valve for proper operation by placing finger over inlet hole in valve end several times. Valve should snap back. If not, replace valve. Refer to "Crankcase Ventilation System," PCV.
^ CHECK: Service Bulletins for updates.
^ CHECK: For broken motor mounts.
^ CHECK: Generator output voltage. Repair if less than 9 volts or more than 16 volts.

IGNITION SYSTEM
^ CHECK: Ignition system; wires, plugs, etc.

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

FUEL SYSTEM

NOTICE: Monitoring long term fuel trim will help identify the cause of the problem. If the system is running lean (long term fuel trim greater than 150), refer to "Diagnostic Aids"Powertrain Controls - ECM/PCM in Diagnostic Trouble Code (DTC) 44. If the system is running rich (long term fuel trim less than 110), refer to "Diagnostic Aids"Powertrain Controls - ECM/PCM in Diagnostic Trouble Code (DTC) 45.

^ CHECK: Fuel injector coil/balance. Refer to CHART C-2A.Chart C-2A Fuel Injector Balance Test
^ CHECK: For fuel in pressure regulator hose. If fuel is present, replace regulator assembly.
^ CHECK: Evaporative Emission (EVAP) control system, use CHART C-3Chart C-3 Evaporative Emission Control System.
^ CHECK: The Heated Oxygen Sensor (H02S) should respond quickly to different throttle positions. If it does not, check the Heated Oxygen Sensor (H02S) for silicon contamination from fuel or improper use of 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.
^ CHECK: Scan tool for injector fault which could indicate one or more faulty injectors or wiring.