Rough, Unstable, or Incorrect Idle, Stalling

CIRCUIT DESCRIPTION
The 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." - When to Use This Section

^ Motor mounts for damage, grounding out on frame, or out of position, etc.

^ 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. Diagnostic Trouble Code Charts / Code 35 or C-Charts Component Testing / C-2B chart. Chart C-2B Idle Air Control (IAC) Valve Check

^ Generator output voltage. Repair if less than 9 or more than 16 volts.

^ Park/Neutral (P/N) switch circuit. Refer to C-charts Component Testing / Chart C-1A or use "Scan" tool and be sure tool indicates vehicle is in drive with gear selector in drive (125C). Chart C-1A Park/Neutral Switch Diagnosis

^ Injector balance. Refer to C-charts Component Testing / Chart C-2A. Chart C-2A Injector Balance Test

^ 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 / Exhaust Gas Recirculation. Service and Repair

^ Evaporative Emission Control System. Refer to C-charts Component Testing / Chart C-3. Chart C-3 Canister Purge Check

^ Power Steering Pressure switch input. The state of the switch should only change when wheels are turned up against the stops. Refer to C-charts Component Testing / Chart C-1E. Chart C-1E Power Steering Pressure Switch (PSPS) Check

^ 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 Refer to C-charts Component Testing / Chart C-10A. Chart C-10A A/C Clutch Control

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. Refer to Fuel System and Air Induction / Adjustments. 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. DTC 44
If the system is running rich (block learn values less than 110) refer to "Diagnostic Aids" for Diagnostic Trouble Code 45. See System Diagnosis / Scan Tester Diagnosis. DTC 45