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.

Is the action complete?

--

Go to Step 4

--

4

  1. Check the TP sensor for binding or sticking. Voltage should increase at a steady rate as the throttle is moved toward wide open Throttle.
  2. Repair the TP sensor if there is a malfunction found.

Was a problem found?

--

Go to Step 16

Go to Step 5

5

  1. Check the MAP sensor for proper operation. Refer to Manifold Absolute Pressure Sensor Output Diagnosis .
  2. Repair if there is a malfunction found.

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 there is a malfunction found.

Was a problem found?

--

Go to Step 16

Go to Step 7

7

  1. Check the Ignition Control Module for proper grounds.
  2. Repair if there is a malfunction found with the grounds.

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 FEB 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.
  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. The generator output voltage should be between the specified values.
  2. If a problem is found, repair as necessary.

Was a problem found?

11V-16 V

Go to Step 16

Go to Step 14

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

Check for Service Bulletins

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