GM Service Manual Online
For 1990-2009 cars only

Hesitation, Sag, Stumble

Step

Action

Value(s)

Yes

No

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

1

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Perform a bulletin search.
  2. If a bulletin that addresses the symptom is found, correct the condition as instructed in the bulletin.

Was a bulletin found that addresses the symptom?

--

Go to Step 16

Go to Step 3

3

Perform the careful visual/physical checks as described at the start of Symptoms section.

Was the visual/physical check performed?

--

Go to Step 4

Go to Important Preliminary Checks

4

Check the TP sensor for binding or sticking. Voltage should increase at a steady rate as the throttle is moved toward wide open throttle.

Was a problem found?

--

Go to Step 16

Go to Step 5

5

  1. Check the MAP sensor for proper operation. Refer Manifold Absolute Pressure Sensor Output Diagnosis .
  2. Repair if found malfunctioning

Was a problem found?

--

Go to Step 16

Go to Step 6

6

  1. Check for fouled spark plugs.
  2. Replace the spark plugs if found malfunctioning.

Was a problem found?

--

Go to Step 16

Go to Step 7

7

  1. Check the Ignition Control Module for a proper ground connection.
  2. Repair if ground is found malfunctioning.

Was problem found?

--

Go to Step 16

Go to Step 8

8

  1. Check for poor fuel pressure. Refer to Fuel System Diagnosis .
  2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 16

Go to Step 9

9

  1. Check for contaminated fuel.
  2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 16

Go to Step 10

10

  1. Perform the Fuel Injector Solenoid Coil Test and Fuel Injector Balance Test .
  2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 16

Go to Step 11

11

  1. Check for proper system performance. Use Table Evaporative Emission Control System Diagnosis .
  2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 16

Go to Step 12

12

  1. Check for proper function of the thermostat. Also check for proper heat range, refer to section 6B.
  2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 16

Go to Step 13

13

  1. Check the generator for proper output voltage.
  2. The generator output voltage should be between the specified values.

Is the voltage between the specified value?

11V-16V

Go to Step 14

Go to Powertrain Control Module Controlled Generator Diagnosis

14

  1. Check the intake valves for valve deposits.
  2. If deposits are found, remove as necessary.

Were deposits found on the intake valves?

--

Go to Step 16

Go to Step 15

15

  1. Review all diagnostic procedures within this table.
  2. If all procedures have been completed and no malfunctions have been found, review/inspect the following items:
  3. • Visual/physical inspection.
    • Scan tool data.
    • All electrical connections within a suspected circuit and/or system.
  4. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 16

--

16

Operate vehicle within the conditions under which the original symptom was noted.

Does the system now operate properly?

--

System OK

Go to Step 2