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 Powertrain Control Module (PCM) grounds for being clean, tight and proper routing.

FUEL SYSTEM CHECKS
^ Injector balance. Refer to CHART C-2A. Chart C-2A Fuel Injector Balance Test
^ For fuel in pressure regulator hose. If fuel is present, replace regulator assembly.
^ Evaporative Emission Control (EVAP) system, use CHART C-3. Chart C-3 EVAP Canister Purge Valve Check
^ The heated oxygen sensor should respond quickly to different throttle positions. If it does not, check the heated oxygen sensor for silicon contamination from fuel or use of improper RTV sealant. The sensor will have a white, powdery coating, and will indicate 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.

NOTICE:
Monitoring L.T. fuel trim and S.T. fuel trim will help identify the cause of some problems. Refer to Typical Tech 1 Data Definitions for an explanation of L.T. fuel trim and ST. fuel trim.

ADDITIONAL CHECKS
^ Throttle linkage for sticking or binding.
^ Exhaust Gas Recirculation (EGR) system, use CHART C-7. Chart C-7 Exhaust Gas Recirculation (EGR) Flow Check
^ Idle Air Control (IAC) operation, use CHART C-2B. Chart C-2B Idle Air Control (IAC) System Check
^ A/C signal to PCM, 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
^ Crankcase ventilation valve for proper operation. Refer to Positive Crankcase Ventilation. Positive Crankcase Ventilation
^ Service Bulletins for PROM updates.
^ For broken motor mounts.
^ Generator output voltage. Repair if less than 9 or more than 17.3 volts.