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
1. Perform careful visual and physical checks as described in preliminary checks. Refer to Computers and Controls / System Diagnosis / Procedures / Diagnosis by Symptom / Preliminary Checks. Testing and Inspection
2. Check For vacuum leaks.
3. Check the Powertrain Control Module (PCM) grounds for being clean, tight and proper routing. Refer to PCM wiring diagrams.

ADDITIONAL CHECKS
1. Check the Manifold Absolute Pressure (MAP) sensor. Refer to Computers and Controls / System Diagnosis / Procedures / Diagnostic Charts / Chart C-1D. Chart C-1D Manifold Absolute Pressure (MAP) Output Check
2. Check the throttle linkage for sticking or binding.
3. Check the transaxle range switch circuit. Use the Tech 1 scan tool and be sure tool indicates gear range selected.
4. Check Idle Air Control (IAC) valve operation. Refer to Computers and Controls / System Diagnosis / Procedures / Diagnostic Charts / Chart C-2B. Chart C-2B Idle Air Control (IAC) System Check
5. Check the Exhaust Gas Recirculation (EGR) valve. There should be no EGR at idle. Refer to Computers and Controls / System Diagnosis / Procedures / Diagnostic Charts / Chart C-7. Chart C-7 EGR System Check
6. Check the A/C request signal to PCM, the 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. Refer to Computers and Controls / System Diagnosis / Procedures / Diagnostic Charts / Chart C-10. Chart C-10 A/C Clutch Control Circuit Diagnosis
7. Check the crankcase ventilation valve for proper operation by placing finger over inlet hole in valve end several times. Valve should snap back. If not, replace the valve.
8. Check Service Bulletins for updates.
9. Check For broken motor mounts.
10. Check Generator output voltage. Repair if less than 9 volts or more than 16 volts.

IGNITION SYSTEM
Check spark plugs, plug wires and ignition components.

ENGINE MECHANICAL
1. Perform a cylinder compression check.
2. Check for the correct camshaft or weak valve springs.

FUEL SYSTEM

NOTE: 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 Computers and Controls / System Diagnosis / Procedures / Diagnostic Charts / Code 44. Powertrain Controls - ECM/PCM If the system is running rich (long term fuel trim less than 110), refer to Computers and Controls / System Diagnosis / Procedures / Diagnostic Charts / Code 45. Powertrain Controls - ECM/PCM

1. Check the fuel injector coil / balance. Refer to Computers and Controls / System Diagnosis / Procedures / Diagnostic Charts / Chart C-2A. Chart C-2A Fuel Injector Balance Test
2. Check for fuel in pressure regulator hose. If fuel is present, replace regulator assembly.
3. Check the evaporative emission control system. Refer to Computers and Controls / System Diagnosis / Procedures / Diagnostic Charts / Chart C-3. Chart C-3 Evaporative Emission Control System
4. Check the Heated Oxygen Sensor (H02S) should respond quickly to different throttle positions. If it does not, check the 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.
5. Check the scan tool for injector fault which could indicate one or more faulty injectors or wiring.