Rough, Unstable, or Incorrect Idle, Stalling
CIRCUIT DESCRIPTIONThe engine runs unevenly at idle. If bad enough, the car may shake. Also, the idle may vary in rpm (called "hunting"). Either condition may be bad enough to cause stalling. Engine idles at incorrect speed.
INSPECTION
^ Perform careful visual check as described in When To Use This Section.
^ Motor mounts for damage, grounding out on frame, or out of position, ect.
^ Throttle linkage for sticking or binding.
^ Throttle Position Sensor (TPS) for sticking or binding, be sure output is stable at idle and adjustment specification is correct.
^ Idle Air Control (IAC) system. See Code 35 or C-2B charts.
^ Generator output voltage. Repair if less than 9 or more than 16 volts.
^ Park/Neutral (P/N) switch circuit. See CHART C-1A or use "Scan" tool and be sure tool indicates vehicle is in drive with gear selector in drive (125C).
^ Injector balance. See Chart C-2A.
^ Positive Crankcase Ventilation ([1][2]PCV) valve for proper operation by placing finger over inlet hole in valve end several times. Valve should snap back. If not, replace valve. See Emission Control Systems.
^ Evaporative Emission Control System, Chart C-3.
^ Power Steering Pressure switch input. The state of the switch should only change when wheels are turned up against the stops. See Chart C-1E.
^ Electronic Control Module (ECM) ground circuits.
^ Exhaust Gas Recirculation (EGR) valve: There should be no EGR at idle.
^ Run a cylinder compression check.
^ Check for fuel in pressure regulator hose. If present, replace regulator assembly.
^ Check ignition system; wires and plugs.
^ If problem exists with A/C "ON," check A/C system operation, Chart C-10B.
IDLE LEARN PROCEDURE
Engine will run rough or stall if loss of battery power to the ECM has occurred. This ECM has an idle learn feature. See Fuel System and Air Induction / Adjustments.
BLOCK LEARN VALUES
Monitoring block learn values may help identify the cause of the problem. If the system is running lean (block learn greater than 150) refer to "Diagnostic Aids" for Diagnostic Trouble Code 44. If the system is running rich (block learn values less than 110) refer to "Diagnostic Aids" for Diagnostic Trouble Code 45. See Scan Tester Diagnosis.