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
- Carburetor spray
- Code reader
- Vacuum gauge
- Protective eye wear 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
- If a malfunction has occurred that the
computer has realized, the check engine or service engine soon light will be
read the trouble codes
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.
Step 2 - Poor fuel pressure can cause the
engine to go "lean" when the throttle is opened. The first check is to
the fuel filter
and check the flow by trying to blow through it, the filter
should flow freely.
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.
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.
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 enrich 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
Fuel Pressure Gauge
Fuel Pressure Regulator
Step 6 - The air intake to the engine is
metered by a mass air flow sensor, this sensor provides feedback data to the
computer which is then processed. If this intake system is allowed to leak it
will cause a misreading making the engine hesitate. Inspect the intake boot for
tears or holes and
Step 7 - The mass air flow sensor is used to
measure the air that travels into the engine. Inside this sensor is a hot wire
that becomes contaminated which inhibits its ability to provide correct
information to the computer. If this sensor has more than 70,000 miles servicing
Replacement Air Intake Boot
can help cure engine hesitation.
Step 8 - The throttle bore is designed to
control the volume of air the engine will ingest. The butterfly and throat of
the bore (plate) becomes contaminated with impurities and must be
Service Mass Air Flow Sensor
much like the mass air flow sensor. Once this condition is corrected the engine
can return to normal operation.
Step 9 - The spark plugs of an engine are
designed to ignite the fuel air mixture inside the combustion chamber to provide
the engine's power. If these spark plugs or maladjusted or worn they can cause
the ignition timing to change causing a hesitation,
remove the spark plugs
Throttle Body Service
Step 10 - The clutch is designed to release the
engine from the transmission, when this part wears it can cause a hesitation in
the motion of the car. To test this condition drive the car at a steady speed,
then very lightly tap the clutch pedal, if the car responds the
clutch is worn
timing belt or
is used to keep the engine crankshaft to camshaft relationship
correct. If this timing becomes misaligned, the engine can experience low power
- A rare occurrence, but it does
happen, if everything has not helped an engine hesitation and low power and the
ignition system is suspect, remove the harmonic balancer to inspect the wood-ruff
key. This key can become worn allowing the ignition trigger to become retarded
causing the engine hesitation.
- An engine hesitation is an interruption of
continuous power during acceleration. When a engine is hesitating it will cause
the car to lunge or surge
which will cause a sudden jerk as the car slows down. This condition can cause dangerous
situations in heavy traffic when drivers behind expect continuous
Older engine's are equipped with a distributor ignition system. This systems
can cause hesitation when maladjusted, by using a
this situation can be checked and corrected. If the timing is
adjusted too far retarded (behind the timing mark) in relationship to the engine
crankshaft it will cause hesitation. If the engine timing is way
off (20 degrees or more) check the timing belt or timing chain, the
Article first published 2017-01-27