GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2000 🢒 Catera 🢒 Engine 🢒 Engine Controls - 3.0L (L81) 🢒 Rough, Unstable, or Incorrect Idle and Stalling

Checks

Action

DEFINITION: The engine runs unevenly at idle. If severe, the engine or the vehicle may shake. Engine idle speed may vary in RPM. Either condition may be severe enough to stall the engine.

Preliminary Checks
    • Refer to Important Preliminary Checks Before Starting in Symptoms .
    • Search for bulletins.
    • Inspect the ECM grounds for being clean, tight and in the proper locations. Refer to Engine Controls Schematics .
    • Remove and inspect the air filter element for dirt, or for being restricted. Refer to Air Filter Element and Air Cleaner Assembly . Replace as necessary.

Fuel System
    • Test the fuel injectors. Refer to Fuel Injector Solenoid Coil Test .
    • Test for incorrect fuel pressure. Refer to Fuel System Diagnosis .
    • Test for a restricted fuel filter. Refer to Fuel System Diagnosis .
    • Test for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Confirm that each injector harness is connected to the correct injector/cylinder. Relocate the injector harnesses as necessary.
    • Inspect for items which can cause an engine to run rich (long term fuel trim near -13 percent). For a rich condition, refer to DTC P0172 Fuel Trim System Rich Bank 1 and DTC P0175 Fuel Trim System Rich Bank 2 .
    • Inspect for items that can cause an engine to run lean (long term fuel trim near 23 percent). For a lean condition, refer to DTC P0171 Fuel Trim System Lean Bank 1 and DTC P0174 Fuel Trim System Lean Bank 2 .

Sensor/System
    • Test the crankcase ventilation valve for proper operation. Place a finger over the inlet hole of the valve end several times. The valve should snap back. If not, replace the valve.
    • Use a scan tool in order to monitor the knock sensor (KS) system for excessive spark retard activity. Refer to Detonation/Spark Knock .

Ignition System
    • Test for proper ignition voltage output with a J 26792 spark tester. Refer to Ignition System Check .
    • Remove the spark plugs and inspect for the following conditions:
       - Correct heat range
       - Wet plugs
       - Cracks
       - Wear
       - Improper gap
       - Burned electrodes
       - Heavy deposits
    • An improper spark plug gap may cause a driveability concern. Gap the spark plugs using a wire gauge gap tool. Refer to Spark Plug Replacement in Engine Electrical.
    • Determine the cause of the fouling before replacing the spark plugs if the spark plugs are gas, coolant or oil fouled. Refer to Spark Plug Visual Diagnosis in Engine Electrical.
       - For diagnosis of a rich condition, refer to DTC P0172 Fuel Trim System Rich Bank 1 or DTC P0175 Fuel Trim System Rich Bank 2 .
       - For diagnosis of coolant contaminated spark plugs, refer to Loss of Coolant in Engine Cooling.
       - For diagnosis of oil fouled spark plugs, refer to Oil Consumption Diagnosis in Engine Mechanical.

Engine Mechanical
    • Inspect engine mechanical for the following:
       - Low compression
       - Sticking or leaking valves
       - Worn camshaft lobes
       - Camshaft timing
       - Broken valve springs
       - Excessive oil in combustion chamber-Leaking valve seals
    • For more information, refer to one or more of the following procedures in Engine Mechanical:
       -  Engine Compression Test
       -  Oil Consumption Diagnosis
    • For incorrect basic engine parts, inspect the following:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.
    • Refer to Engine Mechanical for diagnosis procedures.

Additional Checks
    • Inspect the exhaust system for possible restrictions:
       - The exhaust system components for physical damage
       - The mufflers for heat distress or possible internal failure
       - The catalytic converters for possible plugged pipes by comparing the exhaust system back pressure on each side of engine. Refer to Restricted Exhaust System Check .
    • Electromagnetic interference (EMI) on the reference circuit can cause an engine miss condition. A scan tool can usually detect EMI by monitoring the engine RPM. A sudden increase in RPM with little change in actual engine RPM change indicates that EMI is present. If a problem exists, inspect for high voltage components near ignition control circuits.
    • Test the PNP switch circuit. Refer to DTC P0705 Trans Range Switch Circuit or DTC P0706 Trans Range Switch Performance .
    • Inspect for faulty engine mounts. Refer to Engine Mount Replacement in Engine Mechanical.
    • Inspect the intake manifold and the exhaust manifold passages for casting flash. Refer to Intake Manifold Replacement or Exhaust Manifold Cleaning and Inspection in Engine Mechanical.