Hesitation, Sag, Stumble

WARNING: This page is about a different car, the 2004 Pontiac Aztek and 2004 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.

Inspection/Test	Action
DEFINITION: Momentary lack of response as the accelerator is pushed down. Can occur at any vehicle speed. Usually more pronounced when first trying to make the vehicle move, as from a stop sign. May cause the engine to stall if severe enough.
Preliminary	Refer to Diagnostic System Check - Engine Controls . Refer to Intermittent Conditions before starting. Search for bulletins.
Sensor/System	NOTE: Refer to Silicon Contamination of Heated Oxygen Sensors Notice in Cautions and Notices. Monitor the heated oxygen sensors (HO2S). The heated oxygen sensors should respond quickly to different throttle positions. If not, inspect the HO2S for silicon or other contaminants from fuel or use of improper RTV sealant. The sensors may have a white powdery coating. Silicon contamination causes a high but false HO2S signal voltage, rich exhaust indication. The (PCM) will reduce the amount of fuel delivered to the engine, causing a severe driveability problem. Monitor the 24X crank sensor and the CMP sensor signal present parameters on the 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 CKP A and CMP sensor circuits for intermittents. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Monitor the 3X crank sensor parameter on the scan tool. If the 3X crank sensor parameter is not responding, inspect the CKP sensor B and circuits for intermittents. Inspect the ignition control (IC) circuit, IC timing control circuit, low resolution engine speed signal circuit and the 3X low reference circuit for intermittents. If these circuits become open or shorted they may not set a diagnostic trouble code (DTC) immediately, but are capable of causing driveability complaints. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Test the CKP sensor B for an internal short. Refer to Electronic Ignition (EI) System Diagnosis . Inspect the throttle position (TP) sensor and related wiring. Inspect the mass air flow (MAF) sensor and related wiring. Inspect the air intake ducts for being collapsed, damaged areas, looseness, improper installation, or leaking especially between the MAF sensor and the throttle body. Test the exhaust gas recirculation (EGR) system for proper operation. Refer to Exhaust Gas Recirculation (EGR) System Description .
Fuel System	Test the fuel system circuits for proper operation. Refer to Fuel Pump Electrical Circuit Diagnosis . Test for low fuel pressure. Refer to Fuel System Diagnosis . Test for faulty fuel injectors. Refer to Fuel Injector Balance Test with Special Tool , Fuel Injector Balance Test with Tech 2 , Fuel Injector Coil Test test procedures. Inspect for fuel contamination. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) . 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 .
Ignition System	Inspect for proper ignition voltage output using the following steps: Attach the J 26792 Spark Tester to engine ground. Connect the spark plug end of the spark plug wire to the J 26792 . Leave the other end of the spark plug wire connected to the coil being tested. 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. Crank the engine while observing the J 26792 . A spark should be observed. 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: 5000-8000 Ω (5K-8K Ω) 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: 9 686 Ω per meter (3,000 Ω per foot) 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. Refer to Spark Plug Inspection .