GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2001 🢒 Seville - RHD 🢒 Engine 🢒 Engine Electrical 🢒 Rough, Unstable, or Incorrect Idle and Stalling

Checks

Action

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
    • Refer to Important Preliminary Checks Before Starting in Symptoms - Engine Controls .
    • Search for bulletins.

Sensor/System
    • Check the positive crankcase ventilation (PCV) system for proper operation. Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical.
    • Check the throttle body, and throttle position (TP) sensor for proper operation and damage.
    • Check the knock system (KS) for excessive spark retard.
    • Check the exhaust gas recirculation (EGR) system for proper operation.
    • Check the idle air control (IAC) valve and valve housing for deposits and/or damage.
    • Check for dirty or damaged air cleaner element.
    • Check for collapsed or damage intake air ducting.

Fuel System
    • Check the fuel pressure. Refer to Fuel System Diagnosis .
    • Check the fuel injectors and related wiring. Refer to the following:
    • Check the minimum idle speed.
    • Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Check for items that cause the engine to run rich, or lean.

Ignition System
    • Check the ignition control (IC) circuits for proper connections at each ignition module assembly.
    • Check for proper ignition voltage output using the J 26792 Spark Tester.
    • Check the ignition coils for cracks, or damage.
    • Check for a missing or damaged ignition module assembly grounding spring.
    • Check for misaligned, or damaged spark plug boots.
    • Check the spark plugs. Refer to Spark Plug Inspection

Engine Mechanical
    • Check the following:
       - Engine compression
       - Sticking or leaking valves
       - Worn camshaft lobes
       - Valve timing
       - Worn rocker arms
       - Broken or weak valve springs
       - Excessive oil in the combustion chamber-leaking valve seals.
    • Check for incorrect basic engine parts. Inspect the following:
       - Camshafts
       - Cylinder heads
       - Pistons, etc.

Additional Checks
    • Check the exhaust system for possible restrictions. Refer to Restricted Exhaust
    • Check for fuel loading in the evaporative emission (EVAP) system. Refer to Evaporative Emission System Cleaning .