Hesitation, Sag, Stumble

Definition: Momentary lack of response as the accelerator is pushed down. Can occur at any vehicle speed. Usually most pronounced when first trying to make the vehicle move, as from a stop sign. May cause the engine to stall if severe enough.

1. Was the "On-Board Diagnostic (OBD) System Check" performed?

[YES] Go to Step 2.
[NO] Go to OBD System Check. Initial Inspection

2. a. Perform a bulletin search.
b. If a bulletin that addresses the symptom is found, correct the condition as instructed in the bulletin.
c. Was a bulletin found that addresses the symptom?

[YES] Verify repair.
[NO] Go to Step 3.

3. Was a visual/physical check performed?

[YES] Go to Step 4.
[NO] Go to Visual/Physical Check. Visual/Physical Check

4. a. Check the fuel control Heated Oxygen Sensor (HO2S) 1. The HO2S 1 should respond quickly to different to throttle positions. If it doesn't, check for silicon or other contaminants from fuel or use of improper RTV sealant. The sensors may have a white powdery coating. Silicon contamination sends a rich exhaust signal which causes the Powertrain Control Module (PCM) to command an excessively lean air/fuel mixture.
b. Was a problem found?

[YES] Verify repair.
[NO] Go to Step 5.

5. a. Check the fuel pressure. Refer to Fuel System Pressure Test.
b. Was a problem found?

[YES] Verify repair.
[NO] Go to Step 6.

6. a. Observe the Throttle Position (TP) angle display on the scan tool while slowly increasing throttle pedal.
b. Does the TP angle display steadily increase from 0% at closed throttle to 100% at Wide Open Throttle (WOT)?

[YES] Go to Step 7.
[NO] Go to Step 19.

7. Monitor "Long Term Fuel Trim on the scan tool. Is the "Long Term Fuel Trim" in the negative range (rich condition)?

[YES] Go to Step 8.
[NO] Go to Step 9.

8. a. Check items that can cause the engine to run rich. Refer to Diagnostic Aids in DTC P0172. P0172
b. Was a problem found?

[YES] Verify repair.
[NO] Go to Step 10.

9. a. Check items that can cause the engine to run lean. Refer to Diagnostic Aids in DTC P0171. P0171
b. Was a problem found?

[YES] Verify repair.
[NO] Go to Step 10.

10. a. Check for proper ignition voltage output with spark tester J 26792 (ST-125).
b. Was a problem found?

[YES] Verify repair.
[NO] Go to Step 11.

11. a. Check for a loose ignition control module ground.
b. Was a problem found?

[YES] Verify repair.
[NO] Go to Step 12.

12. a. Visually/physically inspect the secondary ignition wires. Check for the following conditions:
- Verify that all ignition wire resistances are less than the specified value.
- Value that ignition wires are correctly routed to eliminate cross-firing.
- Verify that ignition wires are not arcing to ground. Spraying the secondary ignition wires with a light mist of water may help locate an intermittent problem.
b. Was a problem found?

[VALUES] 30,000 ohms.

[YES] Verify repair.
[NO] Go to Step 13.

13. a. Remove the ignition coil and check for cracks or carbon tracking.
b. Was a problem found?

[YES] Verify repair.
[NO] Go to Step 14.

14. a. Check the ignition coil secondary resistance.
b. Replace the coil if it is not within the specified value.
c. Was a problem found?

[VALUES] 9 k-ohms - 12 k-ohms.

[YES] Verify repair.
[NO] Go to Step 15.

15. a. Remove the spark plugs and check for gas or oil fouling, cracks, wear, improper gap, burned electrodes of heavy deposits.
b. If spark plugs are fouled, the cause of fouling must be determined before replacing the spark plugs.
c. Was a problem found?

[YES] Verify repair.
[NO] Go to Step 16.

16. a. Check the Powertrain Control Module (PCM) grounds to verify that they are clean and tight. Refer to the PCM wiring diagrams.
b. Was a problem found?

[YES] Verify repair.
[NO] Go to Step 17.

17. a. Visually/physically check vacuum hoses for splits, kinks, and proper connections and routing as shown on the "Vehicle Emission Control Information" label.
b. Was a problem found?

[YES] Verify repair.
[NO] Go to Step 18.

18. a. Review all diagnostic procedures within this table.
b. If all procedures have been completed and no malfunctions have been found, review/inspect the following:
- Visual/physical inspection.
- Scan tool data.
- Freeze Frame data/Failure Records buffer.
- All electrical connections within a suspected circuit and/or system.
c. If a problem was found, repair as necessary.
d. Was a problem found?

[YES] Verify repair.
[NO] Contact Technical Assistance.

19. Replace the TP sensor.

[YES] Verify repair.