GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2000 🢒 Grand Am 🢒 Engine 🢒 Engine Controls - 3.4L 🢒 Rough, Unstable, or Incorrect Idle and Stalling

Inspection/Test

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 Intermittent Conditions .
    •  Search for bulletins.

Fuel System
    • Test the fuel pressure. Refer to Fuel System Pressure Test .
    • Inspect 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.
    • Inspect any items which may cause an engine to run rich, long term fuel trim is significantly in the negative range. Refer to Diagnostic Aids for DTC P0172.
    • Inspect any items which may cause an engine to run lean, long term fuel trim is significantly in the positive range. Refer to Diagnostic Aids for DTC P0171.

Sensor/System
    • Inspect for any conditions which cause an incorrect idle speed.
       -  Throttle body tampering--Refer to Fuel Metering System Component Description .
       - Excessive deposits
       - Damage
       -  Restricted air intake system
       -  Large vacuum leak
    • Inspect Crankcase ventilation valve for proper operation. Refer to Crankcase Ventilation System Description .
    • Inspect the TP sensor and related wiring. Refer to DTC P0123 Throttle Position (TP) Sensor Circuit High Voltage .
    • Monitor the 24X crankshaft position and camshaft position sensors on scan tool. If both are not responding, test the sensor feed circuit. Both sensors use a separate feed circuit but are internally connected to power. Test all 24X and CMP sensor circuits for intermittents. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
    • Monitor the 3X parameter on the scan tool. If the 3X is not responding, inspect the 7X CKP sensor and circuits for intermittents. Inspect the IC circuit, Bypass circuit, 3X Reference High Circuit, and the 3X Reference Low circuit for intermittents. If these circuits become open, or shorted may not set a DTC immediately, but are capable of causing driveability complaints. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
    • Inspect the EGR system for proper operation. Refer to Exhaust Gas Recirculation (EGR) System Description .
    • Test the Transaxle Range Switch input with the vehicle in drive and the gear selector in drive or overdrive.

Ignition System
    • Inspect for proper ignition voltage output using the following steps:
        1.  Attach the J 26792 spark tester to engine ground.
        2.  Connect the spark plug end of the spark plug wire to the J 26792 spark tester; leave the other end of the spark plug wire connected to the coil being tested.
        3.  Connect the spark plug end of the companion spark plug wire to ground.

The companion spark plug wire is the wire attached to the corresponding coil tower.

        4.  Crank the engine while observing the J 26792 spark tester; a spark should be observed.
        5.  Repeat the above steps for each coil.
    •  If spark is not present at the coils, inspect for the following conditions:
       -  Coils--Cracks, carbon tracking/arcing, or a resistance value outside the specified range.

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

       -  Spark Plug wires--signs of arcing, cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside the specified range.

Spark Plug Wire Resistance
600ohms per foot (1 968ohms per meter).

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

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

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

Additional
    • Inspect for possible restrictions in the following components:
       - The exhaust system for damaged or collapsed pipes
       - The mufflers for heat distress or possible internal failure
       - The catalytic converter for possible plugged conditions--Refer to Restricted Exhaust and Exhaust Leakage - Not OBD II in Engine Exhaust.
    • Inspect for faulty motor mounts. Refer to Engine Mechanical.
    •  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 in RPM with little change in actual engine RPM change, indicates EMI is present. If a problem exists, inspect the routing of secondary ignition wires, high voltage components--near ignition control (IC) circuits.
    • Inspect for intake and exhaust manifold passages for casting flash. Refer to Base Engine Misfire Diagnosis in Engine Mechanical.