For 1990-2009 cars

#### Hesitation, Sag, Stumble Symptom

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
DEFINITION: A momentary lack of response as the accelerator is pushed down. This condition can occur at any vehicle speed. his condition is usually most pronounced when you first try to make the vehicle move, as from a stop sign. This may cause the engine to stall if the condition is severe enough.
1 | Did you perform the On-Board Diagnostic (OBD) System Check? | -- | 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 present, correct the condition as instructed in the bulletin.

Did you find a bulletin that addresses the symptom?

--

Go to Step 16

Go to Step 3

3 | Did you perform a visual/physical check? | -- | Go to Step 4 | Go to Symptoms
4 |

1. Check the heated oxygen sensors (HO2S). The heated oxygen sensors (HO2S) should respond quickly to the different throttle positions. If the sensors do not respond to the different throttle positions, check the HO2S for silicon or other contaminants from the fuel or the use of the 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 ECM will then reduce the amount of the fuel that is delivered to the engine, causing a severe driveability problem.
2. If a problem is present, repair as necessary.

Did you make a repair?

--

Go to Step 16

Go to Step 5

5 |

1. Check the fuel pressure. Refer to Fuel System Diagnosis .
2. If a problem is present, repair as necessary.

Did you find a problem?

--

Go to Step 16

Go to Step 6

6 | Observe the TP 1 signal display on the scan tool while slowly increasing throttle pedal. Does the TP 1 signal display steadily increase from about 0.33 volt at closed throttle to more than 4.0 volts at WOT? | -- | Go to Step 7 | Go to DTC P1220 Throttle Position (TP) Sensor 2 Circuit
7 | Monitor the Long Term Fuel Trim on the scan tool. Is the Long Term Fuel Trim significantly in the negative range (rich condition)? | -- | Go to Step 8 | Go to Step 9
8 |

1. Check the items that can cause the engine to run rich.
2. If a problem is present, repair as necessary.

Did you find a problem?

--

Go to Step 16

Go to Step 10

9 |

1. Check the items that can cause the engine to run lean.
2. If a problem is present, repair as necessary.

Did you find a problem?

--

Go to Step 16

Go to Step 10

10 |

1. Check the primary connections at the ignition coil assembly. Refer to Wiring Repairs in Wirings Systems for the proper procedure. Also, refer to Checking Terminal Contact in Engine Control Module Diagnosis .
2. If a problem is present, repair as necessary.

Did you find a problem?

--

Go to Step 16

Go to Step 11

11 |

1. Check the ignition coils for any cracks or any carbon tracking.
2. If a problem is present, repair as necessary.

Did you find a problem?

--

Go to Step 16

Go to Step 12

12 |

1. Check the ECM grounds for being clean, tight and in the proper locations.
2. If a problem is present, repair as necessary.

Did you find a problem?

--

Go to Step 16

Go to Step 13

13 |

1. Check the MAF sensor connections.
2. If a problem is present, replace the malfunctioning terminals as necessary. Refer to Wiring Repairs in Wiring Systems for the proper procedure.

Did you find a problem?

--

Go to Step 16

Go to Step 14

14 |

1. Visually/physically check the vacuum hoses for the following conditions:

• | Splits

• | Kinks

• | Proper connections

• | Routing as shown on the Vehicle Emission Control Information label.

2. If a problem is present, repair as necessary.

Did you find a problem?

--

Go to Step 16

Go to Step 15

15 |

1. Review all of the diagnostic procedures within this table.
2. If all of the procedures have been completed and no malfunctions have been found, review/inspect the following items:

• | Perform a visual/physical inspection.

• | The scan tool data

• | The Freeze Frame data

• | All of the electrical connections within a suspected circuit and/or system

3. If a problem is present, repair as necessary.

Did you find a problem?

--

Go to Step 16

Go to Step 3

16 | Operate the vehicle under the same conditions (as closely as possible) as when the original symptom occurred. Is the original symptom still present? | -- | Go to Step 3 | Go to Step 17
17 | Are other driveability symptoms still present? | -- | Go to Symptoms | System OK