Why Does My Car Hesitate when Accelerating?

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Figure out why your car lags when you press the gas
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Your engine relies on three key components: air, fuel, and combustion. These three ingredients work together to generate the power your engine’s pistons need to fire. The air provides the oxygen the gas needs to combust, the fuel provides the material that burns, and the spark plugs generate the spark needed for combustion to occur. But if your car is laggy when you accelerate, it generally indicates that your fuel is too rich or your engine isn’t getting enough fuel at the proper pressure levels. We’ll help you identify what’s causing this issue so that you can resolve it and get back on the road.

Car Hesitating or Jerking When You Accelerate?

Hesitation during acceleration is a general sign that your engine isn’t operating at peak efficiency. You likely have a problem with your air, fuel, and spark mixture. This could be caused by a bad fuel pump, clogged fuel injectors, old filters, or some issue with a sensor. If you rule out engine issues, your transmission may to be blame.

Section 1 of 3:

Causes, Symptoms, & Solutions

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  1. The fuel pump is responsible for pressurizing your fuel lines and sending the fuel from your tank to the engine. If it’s starting to fail or it’s not operating efficiently, your engine won’t have enough fuel to fire properly. When you press the pedal, your acceleration will be laggy as the engine tries to fire without the gas it needs. [1]
    • Additional Symptoms: You hear whining noises, your engine stalls out, you lose power when driving uphill, and your car generally handles like it’s low on gas when it’s not.
    • The Fix: See a mechanic to have the fuel pump inspected and replaced. It’s also possible that the fuel pump itself is fine and that the relay (the electrical switch connected to an aftermarket fuel pump) is on the fritz.
    • The Cost: You’re potentially going to spend $500-1,000 on a new fuel pump. If the relay is to blame, you may only need to spend $300-500.
  2. The fuel injectors are the nozzles that spray fuel through the intake manifold (or throttle body) and into the combustion chambers of the engine. If one (or more) of the injectors is clogged, damaged, or failing, it may not distribute the proper amount of fuel into the engine. This could lead to the hesitating you’re noticing. [2]
    • Just FYI, the fuel injectors don’t actually do the injecting—that’s the fuel pump’s job. The injectors are really just nozzles with valves built-in that open and close as needed.
    • Additional Symptoms: You may have engine misfiring, rough idling, a check engine light on, and poor fuel economy. You may also smell fuel when your vehicle is running if there’s a leak.
    • The Fix: You need new fuel injectors. See a mechanic if you aren’t handy. If you are a bit of a gearhead, you can replace the injectors yourself .
    • The Cost: It’ll likely run $350-800 if you drive a common vehicle. If you have a luxury car or a foreign vehicle, it may run up to $2,500.
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  3. The MAF sensor measures the amount of air entering your engine and then cross-checks that airflow against the fuel injection levels to confirm your engine can function. If the MAF sensor fails, your vehicle will think there is too much air in the engine. As a result, your car will run rich and you’ll have stuttering when you accelerate. [3]
    • Additional Symptoms: Your vehicle stalls, you have a rough idle, your engine is very hard to start, and you experience engine “hiccups” where the vehicle kicks back and forth randomly.
    • The Fix: The MAF sensor either needs to be replaced, or removed from the engine and cleaned .
    • The Cost: Expect to spend under $300 for an MAF replacement or cleaning.
  4. The TPS’s primary goal is to monitor the throttle valve angle and confirm that it’s open at the appropriate angle based on your pedal’s position. If the TPS isn’t calibrated correctly, your gas pedal will respond in strange and unexpected ways when you press it. This may result in your vehicle hesitating when you accelerate. [4]
    • Additional Symptoms: Your vehicle has erratic idling, your check engine light is on, your fuel consumption is higher than normal, and your vehicle handles strangely.
    • The Fix: The TPS probably needs to be recalibrated. In rare cases, the sensor may need to be replaced.
    • The Cost: Calibration is unlikely to cost more than $100—that’s a pretty simple process for a mechanic. If you need a new sensor, expect to spend around $200.
  5. Most vehicles have two fuel filters—one in the fuel tank and one in the main fuel line. These filters are supposed to collect any debris or contamination in the gas to keep it out of your engine and prevent damage. If either of these filters is clogged, it can prevent the fuel from flowing freely into the engine. This restriction can prevent the engine from running properly and cause acceleration hesitation. [5]
    • As a maintenance point going forward, you typically need to change your fuel filters every 30,000 miles (48,000 km).
    • Additional Symptoms: You’ll likely have engine misfires, bad gas mileage, trouble accelerating at any speed, vehicle stalls, or trouble starting your car.
    • The Fix: You probably just need new fuel filters. You can do this yourself if you’re handy , or take the car to a mechanic.
    • The Cost: Expect to pay $70-150 for a mechanic to do this. If you buy the filters and do the work yourself, you’ll only need to buy the filters, which should run $40-50.
  6. The ignition system refers to the components that fire when you turn the key to start the car. This includes the ignition switch, the ignition coil, the distributor, and the spark plugs. These components work together to start the car and maintain the proper fuel-air mixture by converting electrical power from the battery/alternator to the spark plugs. If any of these components is failing, you may notice your car hesitates when you press the pedal. [6]
    • Which component is most likely to blame? Acceleration issues point towards the spark plugs. If the battery, coil, or distributor were to blame, you may not have acceleration problems.
    • Additional Symptoms: Symptoms will vary here depending on what’s wrong, but the big one is going to be trouble starting the car. Beyond that, you may notice engine backfiring, misfiring, or throttling.
    • The Fix: Have a mechanic inspect the ignition system and make repairs as needed.
    • The Cost: Repairs here will vary based on what’s wrong. Replacing a spark plug may only run $100, while rebuilding the ignition system can cost up to $1,000.
  7. The timing belt, also known as the timing chain and serpentine belt, is a rubber band that wraps around several pulleys and gears on the side of your engine. It’s responsible for keeping your engine’s individual components running in perfect harmony. If it’s worn down and slipping or completely snapped off the engine, you will notice serious issues accelerating and getting up to speed.
    • Additional Symptoms: Your car stalls, you lose your power steering, and your alternator begins to stop generating enough energy to keep your dash and headlights on.
    • The Fix: You can either replace the serpentine belt yourself , or take it to a mechanic and have them do it for you.
    • The Cost: A mechanic will likely charge around $150 for this. You can save around $100 if you do this yourself.
  8. A vacuum leak refers to a leak anywhere in the engine’s system where air can enter through an unintended opening. This is problematic because it can throw off the air, fuel, and spark ratio your engine needs to operate efficiently. As a consequence, your car may hesitate or jump unexpectedly when you press the gas pedal. [7]
    • Additional Symptoms: It depends on where the vacuum leak is located, but you can generally expect odd engine behavior and underperformance. Your check engine light is also likely to pop on.
    • The Fix: See a mechanic. Vacuum leaks are usually very hard to diagnose and fix.
    • The Cost: It depends on what needs to be replaced. It could be something minor that only runs you about $150, or it could be bad enough that you need an engine rebuild which runs $2,000-4,000.
  9. Your accelerator has a sensor underneath it that monitors the angle of the pedal. It cross checks that angle with the throttle position sensor and engine data to confirm the engine is behaving the way you intend it to. If the sensor is bad though, your engine may kick, jump, hesitate, or slow down unexpectedly. [8]
    • Additional Symptoms: Normally, you won’t be able to drive with a bad pedal sensor. If it’s partially failing though, the odd acceleration is likely to be the only symptom. You’ll may see a check engine light on your dashboard.
    • The Fix: The sensor likely needs to be replaced. See a mechanic to have them wire a new sensor.
    • The Cost: It depends on the make and model of your car and how accessible the sensor is. On the low end, expect to pay around $100-150. On the higher end, this can cost $600-700.
  10. Your transmission is the only non-engine-related issue that might cause acceleration hesitation. If you ruled out every other potential cause, your transmission is likely failing. The transmission’s job is to convert the power of the engine into rotational power for the wheels. If it’s damaged or starting to fail though, your car may hesitate when you accelerate as the transmission lags behind the engine and struggles to keep up. [9]
    • Additional Symptoms: Your car has trouble shifting gears, your car downshifts due to slipping gears (this causes the hesitation), you smell something burning, your transmission fluid is leaking, and you hear odd sounds coming from your engine bay.
    • The Fix: This could be caused by a number of different issues. Since transmissions are complicated, it’s best to see a mechanic on this one.
    • The Cost: It really depends on what’s wrong. Fixing a transmission belt or topping off the transmission fluid shouldn’t cost more than $200-500. On the high end, a new transmission can run up to $7,000.
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Section 2 of 3:

Can you drive if your car hesitates when accelerating?

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  1. This is 100% not an issue you can ignore for long—especially if your check engine light is on—but so long as you’re able to safely navigate and drive, it’s okay to drive to the mechanic. However, if you cannot safely accelerate and it makes driving difficult, don’t push your luck by trying to drive. Get the car towed to the mechanic. [10]
    • Exceptions: There are two scenarios where you shouldn’t drive no matter what. First, if you think your transmission is to blame, don’t drive. You could do seriously expensive damage if you push things. Second, if your vehicle smells like fuel or you see any leaks, don’t turn the car on. It’s a potential fire hazard (and very bad for the environment).
Section 3 of 3:

Car Hesitation and Speed

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  1. If the hesitation during acceleration primarily occurs at lower speeds (or even from stop), it’s more likely that fuel delivery is causing the problem. As the car gets up to speed, the flow of fuel may be smoothing out as the pressure increases from the fuel pump. [11]
    • A note on speed and hesitation: This is not an airtight diagnostic tool. A vehicle with fuel issues may only hesitate at higher speeds, for example. But, this can help narrow things down if the speed seems very closely linked to the onset of your vehicle’s symptoms.
  2. If your vehicle only hesitates to accelerate when you’re at higher speeds, it’s more likely you have a vacuum leak or an issue with your MAF sensor. When fuel can’t combust, your engine will run rich and you’ll have trouble sustaining higher speeds.
  3. If you notice the hesitating occurs when the RPM dial kicks back and your vehicle changes gears, your transmission is probably the issue. The transmission is solely responsible for gear shifts, so any problems that pop up during gear changes scream “transmission problem.” [12]
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      References

      1. ↑ https://www.motortrend.com/how-to/bad-fuel-pump-symptoms/
      2. ↑ https://www.motortrend.com/how-to/1603-diagnosing-a-failed-or-clogged-fuel-injector-on-corvette/
      3. ↑ https://car-repair.carsdirect.com/car-repair/how-to-tell-if-you-have-a-faulty-mass-airflow-sensor
      4. ↑ https://carorbis.com/blog/throttle-position-sensor/
      5. ↑ https://oilchangers.com/blog/signs-of-a-bad-fuel-filter/
      6. ↑ https://stevesimports.com/blog/warning-signs-of-ignition-system-failure/
      7. ↑ https://www.telletire.com/what-is-a-vacuum-leak/
      8. ↑ https://www.hella.com/techworld/us/Technical/Sensors-and-actuators/Accelerator-pedal-sensor-3851/
      9. ↑ https://www.cbac.com/grand-parkway/media-center/blog/2017/march/transmission-trouble-10-warning-signs-you-need-r/
      1. ↑ https://www.griffinsautorepair.com/tow-or-drive-vehicle/
      2. ↑ https://vatire.com/car-maintenance-tips/what-happens-when-a-fuel-pump-goes-out/
      3. ↑ https://www.cbac.com/grand-parkway/media-center/blog/2017/march/transmission-trouble-10-warning-signs-you-need-r/

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