GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2000 🢒 Camaro 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 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 Checks
    • Refer to the Symptoms .
    • Search for bulletins.

Fuel System
    • Test the fuel pressure.
       - Refer to Fuel System Pressure Test .
    • test for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Inspect for fuel in the pressure regulator vacuum hose.
    • Ensure each injector harness is connected to the correct injector/cylinder. Refer to Engine Controls Schematics .
    • Test items which can cause an engine to run rich (long term fuel trim is significantly in the negative range). Refer to Diagnostic Aids for DTC P0172 Fuel Trim System Rich Bank 1 .
    • Test items that can cause an engine to run lean (long term fuel trim is significantly in the positive range). Refer to Diagnostic Aids for DTC P0171 Fuel Trim System Lean Bank 1 .

Sensor/System
    • Inspect for conditions which cause an incorrect idle speed.
       - Throttle body tampering, excessive deposits, or damage.
       - Restricted air intake duct or dirty air cleaner element. Refer to Air Cleaner Element Replacement .
       - Large vacuum leak.
    • Inspect the crankcase ventilation valve for proper installation. Refer to Crankcase Ventilation System Inspection .
    • Test the ETC and inspect related wiring.
    • Test the EGR system for proper operation. Refer to DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient .
    • Test the transaxle range switch input with the vehicle in drive and the gear selector in drive or overdrive.

Ignition System
    • Test for proper ignition voltage output using the following steps:
       - Clip the J 26792 spark tester to engine ground.
       - Connect one end of a spark plug wire to the spark tester, leave the other end of the spark plug wire to the coil being tested.
       - Connect one end of another spark plug wire to the other coil tower, connect the other end of the spark plug wire to ground.
       - Crank the engine while observing the spark tester, a spark should be observed.
       - Repeat the above steps for each coil.
    • If adequate spark is not present at the coils, test for the following conditions:
      • Coils - Cracks, carbon tracking/arcing, or a resistance value outside the specified range.

Coil Secondary Resistance
5000 - 8000 ohms (5K - 8K ohms)

      • Spark Plug wires - Signs of arcing/cross firing, cracks, carbon tracking, plug boot damage, pinched, incorrect routing, or a resistance value more than the specified value.

Spark Plug Wires Resistance
3280-4921 ohms/meter(1000-1500 ohms/ft).

   Important: Spraying the secondary ignition wires with a light mist of water may help locate an intermittent problem. Ignition components will arc to ground when a secondary component is malfunctioning.

      • Malfunctioning ignition control module.
      • Ignition System Wiring - Loose ignition module feed or ground connection, or damaged system wiring.
    • Remove spark plugs and test for the following conditions:
       - Fouled plugs
       - Cracks
       - Wear
       - Incorrect gap
       - Burned or damaged electrodes
       - Incorrect heat range
    • If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.

Engine Mechanical
    • Test the following:
       - Engine compression
       - Sticking or leaking valves
       - Worn camshaft lobes
       - Valve timing
       - Bent push rods
       - Worn rocker arms
       - Broken valve springs
       - Excessive oil in combustion chamber-Leaking valve seals
    • For incorrect basic engine parts. Inspect the following:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.
    • Refer to Base Engine Misfire Diagnosis in Engine Mechanical.

Additional Tests
    • Test the exhaust system for a possible restriction.
       - Inspect exhaust system for damaged or collapsed pipes.
       - Inspect mufflers for heat distress or possible internal failure.
       - For possible plugged Three-Way catalytic converter. Refer to Restricted Exhaust System Check .
    • Inspect for loose, worn, or broken motor mounts.
    • An engine miss condition can be caused by Electromagnetic Interference (EMI) on the reference circuit. EMI can usually be detected by monitoring engine RPM with a scan tool. A sudden increase or decrease in RPM with little change in actual engine RPM indicates that EMI is present. Inspect for incorrect routing of secondary ignition wires. Also inspect the ignition coils for cracks, carbon tracking, or signs of arcing.
    • Inspect for intake and exhaust manifold passages for casting flash.