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 in "Preliminary Checks."

^ CHECK: For vacuum leaks.
^ CHECK: PCM grounds for being clean, tight and proper routing. See PCM wiring diagrams.
^ CHECK: Service Bulletins for EPROM updates.

IGNITION SYSTEM

^ CHECK: Ignition system. Spark plugs and ignition components. Refer to "Electronic Ignition (El) System."

ENGINE MECHANICAL

^ CHECK: Perform a cylinder compression check.
^ CHECK: For correct camshaft.

FUEL SYSTEM

^ CHECK: Monitoring long term fuel trim will help identify the cause of the problem.
If the system is running lean (long term fuel trim near 198), refer to "Diagnostic Aids" of DTC 44 chart. Powertrain Controls - ECM/PCM
If the system is running rich (long term fuel trim near 58), refer to "Diagnostic Aids" of DTC 45 chart. Powertrain Controls - ECM/PCM
^ CHECK: Injector balance. Refer to CHART C-2A. Chart C-2A Injector Coil Test Procedure
^ CHECK: For fuel in pressure regulator hose. If fuel is present, replace regulator assembly.
^ CHECK: Evaporative Emission (EVAP) control system, use CHART C-3. Chart C-3 Evaporative Emission Control System
^ CHECK: The Oxygen Sensor (O2S). The O2S should respond rapidly to the varying quantities of oxygen in the exhaust system. After the O2S has reached operating temperature, the voltage should change quickly, and can go as high as 1 volt and as low as 0.1 volt in less than a second. If this response time is slow or voltage is at a steady level, the O2S should be checked for silicon, glycol or other contamination. The O2S may have a white powdery coating (silicon contamination) or a green coating (glycol contamination) that would result in a false signal voltage to PCM, may lead to a driveability complaint.

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: Park/Neutral Position (PNP) switch or trans range switch circuit. See CHART C-1A, or use Tech 1 scan tool and be sure tool indicates vehicle is in drive with gear selector in drive or overdrive (if equipped).
^ CHECK: IAC valve operation, use CHART C-2C. Chart C-2C Idle Air Control (IAC) System Check
^ CHECK: A/C 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 CHART C-10. Chart C-10 A/C Clutch Control Circuit Diagnosis
^ CHECK: For broken motor mounts.
^ CHECK: Generator output voltage. Repair if less than 9 or more than 16 volts.
^ CHECK: For intake valve deposits.