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 the engine.

PRELIMINARY CHECKS
Perform the visual and physical checks in Preliminary Checks. Diagnosis By Symptom/Preliminary Checks.

Check: For vacuum leaks.
Check: Powertrain Control Module (PCM) grounds for being clean, tight and proper routing. Refer to PCM wiring diagrams.

FUEL SYSTEM
Monitoring the long term fuel trim will help identify an excessively lean or rich condition.

Lean Condition
A lean condition is present when the long term fuel trim value reads near 150. Refer to "Diagnostic Aids" located in Code 44 Heated Oxygen Sensor (HO2S) Circuit (Lean Exhaust). Under Diagnostic Trouble Code (DTC) Charts/PCM DTCs. Powertrain Controls - ECM/PCM


Rich Condition
A rich condition is present when the long term fuel trim value reads near 110. Refer to "Diagnostic Aids" located in DTC 45. Refer to Code 45 Heated Oxygen Sensor (HO2S) Circuit (Rich Exhaust). Under Diagnostic Trouble Code (DTC) Charts/PCM DTCs. Powertrain Controls - ECM/PCM


Check: Injector balance. Refer to Chart C-2A Fuel Injector Test Procedure. Under Diagnostic Charts/C Charts. 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. See Chart C-3 Evaporative Emission Control Check. Under Diagnostic Charts/C Charts. Chart C-3 Evaporative Emission Control System
Check: The Heated Oxygen Sensors (HO2S) should respond quickly to different throttle positions. If they don't, check the HO2S for silicon contamination from fuel, or use of improper RTV sealant. The sensors will have a white powder 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.

IGNITION SYSTEM
Check: Ignition system: wires, plugs, ect.

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

ADDITIONAL CHECKS
Check: Manifold Absolute Pressure (MAP) sensor. See Chart C-1D MAP Output Check. Under Diagnostic Charts/C Charts 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: Idle Air Control (IAC) operation. Refer to Chart C-2B Idle Air Control Valve Check. Refer to C Charts. Chart C-2B Idle Air Control (IAC) System Check
Check: Exhaust Gas Recirculation (EGR) valve. There should be no EGR at idle. Refer to Chart C-7 EGR System Check. Refer to C Charts. Chart C-7 EGR System Check
Check: A/C signal to PCM. Tech 1 scanner should indicate A/C is being requested whenever A/C is selected. If problem exists with A/C "ON," check A/C system operation. Refer to Chart C-10 A/C Clutch Circuit Diagnosis. Refer to C Charts. Chart 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 Positive Crankcase Ventilation (PVC). Under Emission Control Systems. Positive Crankcase Ventilation
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.