Most motorists come to know their vehicles quite well, both inside and out. Because of this, it comes as no surprise that most vehicle owners quickly recognize any drivability issue that presents itself.
Of these driveability issues, few can be as aggravating, or difficult to pinpoint as that which could best be described as a jerking, stuttering, or hesitation.
It can be quite maddening to contend with an issue that suddenly occurs, without any perceivable logic. Luckily, the root cause of such issues is seldom difficult to remedy and can be detected quite easily if one only knows where to begin their search.
The following are the most common causes of a car jerking while accelerating and under other driving conditions.
When Accelerating (at Low Speeds)
1) Faulty Ignition Components
A gasoline engine requires a spark to be distributed to each cylinder at the appropriate time, in order to operate efficiently. If a vehicle’s ignition system is compromised, a jerk or hesitation often results, especially at low speeds.
The most common causes of such issues are worn or fouled spark plugs, damaged plug wires, and externally arcing coil packs.
2) Dirty Fuel Injectors
An internal combustion engine is also reliant upon sufficient fuel delivery for proper operation. If an engine’s fuel injectors become clogged, fuel flow can become restricted on one or more cylinders.
When this occurs, rough acceleration can result, with or without the onset of a check engine light.
3) Impeded Intake Air Flow or Faulty MAF Sensor
Combustion within any engine is also dependent upon the intake of fresh, oxygen-dense air. Any condition which prevents adequate delivery of air into a vehicle’s intake can lead to jerking when under a load.
A dirty or severely clogged air filter is often the culprit in such situations. Likewise, a faulty mass air flow sensor can cause similar issues, as a vehicle’s PCM is unable to obtain proper intake figures.
4) Clogged Catalytic Converter
A vehicle’s catalytic converter is responsible for breaking down harmful exhaust gasses that are expelled as a byproduct of combustion. However, a clogged catalytic converter can restrict the outflow of exhaust, thereby stifling engine performance.
In many cases, this will lead to hesitation when under acceleration. A clogged catalytic converter will often be accompanied by a smell of rotten eggs.
5) Worn Throttle Cable
If your vehicle features a cable-driven throttle plate, the typical wear of such a cable can be behind your car’s acceleration issues. When a metal throttle cable begins to fray, it can intermittently hang within its sleeve, causing excessive resistance.
When Accelerating (at High Speeds)
6) Ignition System Issues
When accelerating, any number of irregularities within an engine’s ignition system can lead to jerking and hesitation. This includes a spark plug, plug wire, coil pack, coil, and distributor related issues.
Due to a momentary loss of spark, incomplete combustion occurs, which results in an abnormal engine lope.
7) Fuel System Issues
If an engine is starved for fuel, it cannot operate in an optimum manner, especially when under significant demand during periods of acceleration or at high speed.
A weak fuel pump, restricted fuel filter, and dirty injectors are all common causes of such issues.
8) Restricted Air Intake
Under periods of high-speed acceleration, a vehicle’s engine consumes large quantities of air through its intake to facilitate combustion. If this airflow is interrupted, severe driveability issues typically occur.
A heavily soiled air filter tends to be the most likely cause of such issues, though intake duct damage is also a prime culprit.
9) Engine Misfire
An engine can hesitate, jerk or stutter while cruising for any of the same reasons that such an issue would occur when accelerating. The most likely culprit behind issues of this nature is a misfire on one or more cylinders.
The source of a misfire will typically be rooted in an ignition or fuel system related issue. To determine the source of a misfire, each cylinder will need to be checked for proper spark, and proper fuel pressure should be validated.
10) Faulty Mass Air Flow Sensor
A faulty mass air flow sensor is another common cause of driveability issues that are experienced while cruising. When an engine’s PCM is unable to obtain valid MAF sensor feedback, it is unable to calculate fuel delivery as intended.
11) Damaged Clock Spring Wiring
If jerking only occurs with cruise control engaged, it is possible that a damaged clock spring is the source of your issue.
A clock spring is a wound electrical pigtail that is mounted to a vehicle’s steering wheel. This specialty pigtail facilitates the function of steering wheel-mounted accessories that are constantly in rotation.
When a clock spring becomes worn, an intermittent open in the cruise control circuit wiring can occur.
12) Warped Rotors
Disc brakes rely upon friction between a set of brake pads and their corresponding rotor to slow a vehicle’s progress. Unfortunately, these components do not last forever and replacement is inevitable.
Aging brake rotors tend to be susceptible to warpage, especially when they have been turned on a brake lathe in the past. As a rotor thins, thermal shock from overheating or rapid cooling can lead to a jerking sensation when the brake pedal is applied.
13) Air in ABS System
Modern vehicles utilize an ABS module to vary brake pressure in the event of a panic stop, thereby preventing skidding from occurring. However, proper operation of an ABS system is dependent upon the complete absence of air.
If your car has recently undergone brake work and is now exhibiting abnormal braking characteristics, it is possible that all air has not been properly bled.
14) Low Transmission Fluid
An automatic transmission relies upon an ample supply of transmission fluid to facilitate torque converter operation. If your vehicle’s transmission fluid is low, or in poor condition, hard or delayed shifts often occur.
If a vehicle’s transmission is operated with a lower than the specified fluid level for an extended period of time, lasting damage can result.
15) Faulty Sensors or Solenoids
Automatic transmissions utilize a series of sensors and solenoids to maintain proper shift points. If any of these sensors or solenoids were to become compromised, delayed or erratic shifting will almost always result.
In many cases, such issues will be most prevalent during first gear to second gear shifts, or shifts into overdrive.
16) Vacuum Issues
Many older automatic transmissions featured a vacuum modulator valve. If vacuum supply to this valve was compromised, or the valve itself failed internally, many shift related issues often presented themselves.
17) Damaged or Worn Internal Components
Both automatic and manual transmissions are prone to internal wear with time. As components age, failure can occur, leading to a host of driveability related issues.
Automatic transmissions are often prone to clutch pack related issues, while manual transmissions experience clutch, synchronizer, or geartrain failures.
When Backing Up
18) U-Joint Slack
If your vehicle jerks suddenly when shifted into reverse, you might be experiencing the byproduct of worn driveline components.
Every vehicle will take up a certain amount of slack when shifted into reverse. However, badly worn u-joints can exacerbate this condition, leading to a noticeable jerk as your vehicle first moves rearward.
19) Transmission-Related Issues
It is possible for aging transmissions to jerk and hesitate when being placed in reverse. This can come as a result of several different issues.
The transmission itself might be low on fluid, a solenoid in the valve body could be sticking, or there is a slight chance that internal gearbox wear has occurred.
20) Moisture Under Distributor Cap
An engine’s distributor is responsible for sending spark to each spark plug wire at the appropriate time. However, a cracked distributor cap or faulty distributor cap seal can lead to water ingress.
When water finds its way beneath a vehicle’s distributor cap, misdirected spark and poor idle often result. Problems of this nature tend to show themselves during periods of cold weather, or when it has been raining extensively.
21) Worn or Damaged Spark Plugs or Wires
Additionally, other ignition system components can be responsible for a jerking sensation when a vehicle is at idle. This is most often observed when faced with worn/fouled spark plugs or damaged spark plug wires.
22) Restricted Fuel Flow
Without consistent fuel delivery, an engine cannot perform at its optimum level. Therefore, any issue that compromises a vehicle’s fuel system, can cause issues related to an abnormal idle.
The root cause of such issues can include dirty fuel injectors, a failed fuel pressure regulator, or a clogged fuel filter.
23) Faulty IAC Valve
When at idle, a vehicle’s throttle plate closes, and air distribution is relegated to the engine’s air idle control valve. This valve allows a small amount of air to bypass the throttle plate, in order to sustain engine idle.
If an IAC valve were to fail or become clogged, a harsh or erratic idle could result.
24) Vacuum Leaks
Unmetered air of any type that is allowed to enter your engine’s intake can cause significant idle related issues. This is most commonly referred to as a vacuum leak.
Vacuum leaks often occur at hoses, intake ducting, and intake related gaskets (intake manifold gasket, throttle body gasket).
When the A/C is On
25) Faulty IAC Valve
When engaged, an A/C compressor puts a significant load on a vehicle’s engine. To offset issues related to stalling and poor performance, many vehicles depend upon their air idle control to increase available air for combustion.
When an air idle control valve fails, a limitation of air can cause irregular idle and poor acceleration.
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