Step by step guide on how to repair an engine hesitation when the throttle is depressed, this information pertains to all internal combustion engines.

Difficulty Scale: 4 of 10

Tools and Supplies Needed

  • Flashlight
  • Screwdriver
  • Carburetor spray
  • Code reader
  • Vacuum gauge
  • Protective eyewear and gloves.

Begin by parking the vehicle on level ground, in park with the emergency brake on. The engine will be running in many of these tests so use necessary safety precautions.

Step 1 - If a malfunction has occurred that the computer has realized, the check engine or service engine soon light will be illuminated. First read the trouble codes and then define them to determine the repair needed. Many times an engine can hesitate without the computer detecting a problem, if this is the case proceed to the next step.

Code Reader

Step 2 - Poor fuel pressure can cause the engine to go "lean" when the throttle is opened. The first check is to remove the fuel filter and check the flow by trying to blow through it, the filter should flow freely.

Fuel Filter

Step 3 - The engine depends on a sealed system to contain vacuum the engine creates while running. If this vacuum system develops a leak it can cause the computer to react on false data resulting in a hesitation. Inspect the system and repair any vacuum  lines that are damaged.

Vacuum Leak

Step 4 - The engine's fuel system must operate at a specific pressure, if this pressure is inadequate the engine will hesitate. Locate the fuel pressure test port or use a fuel filter adapter to connect a fuel pressure gauge and check the reading.

Fuel Pressure Gauge

Step 5 - The fuel system pressure regulator is designed to increase the fuel pressure when the throttle is depressed. This pressure increase is used to richen the fuel mixture when the engine is under load. Though some vehicles utilize an internal regulator located at the fuel pump (in tank) others are located at the engine fuel rail which can be tested much easier.

Fuel Pressure Regulator


Written by
Co-Founder and CEO of
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


Please use our question form if you have a specific question about your car as we are not able to give you a full answer on this page.

Article first published (Updated 2015-01-09)