6 Reasons Your Car Hesitates When Accelerating (and Costs to Fix)
Pressing on the gas pedal and instead of instant power, your engine sputters and leaves you lagging? Don’t assume the worst just yet. Sluggish acceleration is sometimes an easy DIY fix.
Continue reading to learn the common causes for hesitation under acceleration before your mechanic starts unnecessarily replacing parts. But don’t simply ignore the problem since inconsistent and unpredictable acceleration is a bigger danger than you may think.
What is Engine Hesitation?
Engine hesitation is when your car temporarily loses power or stumbles when you press the accelerator pedal. Unlike a complete stall, hesitation is a momentary lack of response, almost like your car is “hiccupping” when you try to speed up.
The most frequent sign of engine hesitation is a noticeable lag or delay between pressing the gas pedal and your car responding. Your engine might feel like it’s “missing” or momentarily losing power.
This can happen from a complete stop, while already moving, or when trying to pass another vehicle. If you’ve ever driven a manual transmission car in too high a gear, you probably understand what it feels like.
Some drivers also notice their car surging slightly or feeling jerky during steady acceleration. In cold weather, hesitation might be more pronounced until your engine warms up.
Common Causes of Hesitation When Accelerating
#1 – Dirty/Faulty Mass Airflow Sensor (MAF)
A mass airflow sensor monitors how much air enters the engine and helps your car’s computer determine the correct amount of fuel needed for optimal performance (the ideal air/fuel ratio). When the MAF sensor gets dirty or fails, it sends incorrect readings, causing your engine to receive either too much or too little fuel from its injectors.
The good news is that cleaning the MAF sensor often fixes the problem and it’s a simple task many car owners can do on their own using a specialized MAF sensor cleaner (I personally use CRC cleaner). However, if cleaning doesn’t solve the issue, the sensor likely needs replacement.
Other signs of a bad MAF sensor include rough idling, stalling shortly after starting, and unusually high or low idle speeds. Your check engine light will usually illuminate when the MAF sensor malfunctions, often with specific error codes that help identify the problem.
Cost to Fix:
If the MAF sensor is simply dirty or clogged and requires a good cleaning, expect to pay $10-20 for a mass airflow sensor cleaner spray and a few minutes of your time.
If replacement is necessary, expect to pay between $100-400 total. The sensor itself typically costs $30-300, while labor adds another $70-100. Some European and luxury vehicles may have higher parts costs, pushing the total closer to $500.
Before purchasing a new MAF sensor or making a service appointment, use an OBD2 scan tool to confirm if the MAF sensor is the problem. Many local auto parts stores will even scan your car for free.
#2 – Clogged Fuel Filter
Your fuel filter has one job and that’s to act as a defensive barrier, trapping rust, dirt, and debris before they can reach your engine’s fuel system. Over time, these contaminants build up and start to restrict the flow of fuel. When your fuel filter becomes clogged, your engine struggles to get enough fuel during acceleration, leading to hesitation.
Most modern vehicles can go 40,000-80,000 miles between fuel filter replacements (some even longer). This is a big improvement over older vehicles which typically had 20,000-40,000 mile replacements schedules. The best thing to do is follow your vehicle manufacturer’s recommendation for replacement interval.
Signs of a clogged filter often appear gradually. You might notice worse performance on hills first, followed by hesitation during normal acceleration. If you let it go on long enough, you may experience random stalling or difficulty starting your car.
If you don’t remember the last time the fuel filter was replaced, there’s good possibility that may be the cause of hesitation.
Cost to Fix:
Fuel filter replacement is one of the more affordable repairs, typically costing between $70 to $160 total to have a shop do it for you. The filter itself usually runs $10 to $50, so it may be a scenario where the labor costs more than the part.
Some vehicles have easy-to-access filters that new DIYers can replace themselves, saving on labor costs. However, many modern vehicles have the filter integrated into the fuel pump assembly, which can make replacement more complex and expensive.
#3 – Bad Spark Plugs
Spark plugs create the electrical spark that ignites the air-fuel mixture in your engine’s cylinders. When spark plugs wear out or become fouled with carbon deposits, they can’t produce a strong enough spark for proper combustion. This weak spark is particularly noticeable during acceleration when your engine needs it the most.
Old or worn spark plugs often show multiple symptoms besides hesitation. You might experience a rough idle, bad gas mileage, and difficulty starting (especially when it’s cold out). The problem usually develops gradually, making it easy to overlook until performance significantly degrades.
Many good, modern spark plugs can easily last 50,000 to 80,000 miles or more. But in all cases, they still wear down. They may still work but just not very well. Checking your spark plugs’ condition can also reveal other engine problems, as their appearance changes based on running conditions.
Cost to Fix:
A complete spark plug replacement typically costs between $200 to $300 for most four-cylinder engines. The plugs themselves cost $5-$20 each, depending on type and quality. Labor usually runs $100-$250, though costs can double for V6 or V8 engines where there are more plugs and they may be harder to access.
It’s not unheard of to get a $900 quote from a dealership. But if that’s the case, an independent mechanic will likely be much less for the same work being done.
DIY spark plug replacement is possible on many vehicles, but there’s always a possibility of a plug breaking during removal or even falling into the cylinder. If that happens, a fairly simple job just became complex.
#4 – Bad Fuel Injectors
Fuel injectors are designed to spray a fine, precise mist of fuel into your engine’s cylinders according to exact timing and patterns. Over time, these injectors can become clogged with carbon deposits or wear out, disrupting their spray pattern. When this happens, fuel doesn’t atomize properly, leading to incomplete combustion and hesitation during acceleration.
The most common issue is clogged injectors, which often occurs gradually from low-quality fuel or skipped maintenance. You’ll first start noticing minor issues like hesitation or rough idling before the problem becomes more serious.
Using high-quality fuel with detergents and periodic use of fuel injector cleaners can significantly extend injector life. Many drivers successfully restore performance using fuel injector cleaning services (professional or DIY) before requiring full replacement.
Cost to Fix:
Professional fuel injector cleaning services cost $50-150. If cleaning doesn’t solve the problem, replacement costs vary significantly. A single injector runs $50-150, but labor can add $200-400 for the entire job.
Most mechanics recommend replacing all injectors at once if one fails, which can total $600-1,200 for parts and labor on a four-cylinder engine. If you have a six or eight-cylinder engine, plan on spending more. This is one of those jobs that it pays to get multiple quotes.
#5 – Bad Fuel Pump
The fuel pump’s primary function is delivering gasoline from your tank to the engine with precise pressure and timing. Located either inside or just outside your fuel tank, this pump works constantly while your engine is running. When a fuel pump starts to fail, it can’t maintain the correct fuel pressure your engine needs for proper acceleration.
You’ll typically notice problems first when accelerating up hills or trying to pass other vehicles at highway speeds. Sometimes, your fuel pump will give you an early warning such as a whining noise from the back of your car or your engine may occasionally sputter even during normal driving.
In severe cases, your car may even completely stall, especially after climbing steep hills or during hot weather when the pump is under more stress.
Cost to Fix:
A fuel pump replacement typically costs between $250 to $1,200, but may go up as high as $1,500 (or more) in some vehicles. The part itself ranges from $100 to $600, while labor usually runs $150 to $600.
If just the fuel pump relay needs replacement, expect to pay $50 to $150 total although it’s often an easy DIY replacement with a $25 part.
Related: Signs of a Bad Fuel Pump Control Module
#6 – Throttle Position Sensor (TPS)
The throttle position sensor monitors how far you’re pressing the gas pedal and the position of your throttle plate, sending this data to your car’s computer. Based on these signals, the computer adjusts the air-fuel mixture and engine timing.
When the TPS malfunctions, your car’s computer receives incorrect information about how much power you’re requesting, resulting in hesitation, uneven acceleration, and other issues.
Modern vehicles typically use multiple position sensors for redundancy and safety. Common signs of a failing TPS include sudden changes in engine speed while maintaining a steady gas pedal position, difficulty maintaining constant speed while cruising, and unexpected idle speed changes.
Your check engine light will usually illuminate when there’s a TPS problem, often accompanied by your car entering “limp mode” (a safety feature that prevents engine damage). Unlike some gradual failures, TPS problems often appear suddenly.
Related Trouble Codes: Code P0122, Code P2138
Cost to Fix:
TPS replacement typically costs between $150 to $350 total. The sensor itself ranges from $75 to $250, with labor adding another $75 to $150. Some vehicles combine the TPS with the throttle body assembly, which can increase costs to $500-800 total.
Related Issues and Additional Symptoms
Several other engine problems can create symptoms similar to hesitation or occur alongside it. Understanding these may help pinpoint the exact problem and prevent misdiagnosis.
Vacuum Leaks
Small cracks or loose connections in vacuum lines can create air leaks that disrupt your engine’s air-fuel mixture. Vacuum leaks often cause hesitation during light acceleration but improve under heavy throttle.
Carbon Buildup
Modern direct-injection engines are particularly prone to carbon accumulation on intake valves. This buildup develops gradually, causing rough running, hesitation, and loss of power.
Transmission Issues
Sometimes what feels like engine hesitation is actually a transmission problem. If you notice hesitation mainly during gear changes or feel a delay between pressing the gas and feeling acceleration, have your transmission fluid checked.
Temperature-Related Problems
If hesitation only occurs when your engine is cold or during specific weather conditions, this can help narrow down the cause:
- Cold-weather hesitation often means fuel delivery or spark plug problems.
- Hot-weather issues typically point to fuel pump or vapor lock problems.
- Humidity-related hesitation might suggest ignition system weakness
He’s known for his attention to detail and problem-solving skills and enjoys coming up with out-of-the box solutions when the situation requires it.
When he's not troubleshooting customers' cars, you'll most likely find him working on his current project ('96 Bronco) or cooking Italian food for his family.
Thank for the information. This was very helpful! I knew that it had to do with ineffective air-to-fuel mixture, but you mentioned other items for which to inspect. Will have our local mechanic look into this. Thanks again!
Bad Fuel Injectors
Excellent suggestions. However won’t the on board computer report any defective sensors. Like the fuel pump, Mass flow, Throttle position
Often, but maybe not always.
This is helpful and especially the comment on the hesitation when going uphill. I hope the 2014 pathfinder I have won’t be too costly to repair
Thanks WE are due for an oil change so of course I will mention the problem to the best mechanic in the world. My guy is the one .Thanks again Cyndi
2011 camry 366k miles all stock never change anything. Going to change the coil and spark plugs (last done 40k ago) this weekend and if it doesn’t help with lacking of power going uphill issue, fuel filter and fuel pump is next. This article is helpful.
Glad you found it useful, Larry.
Our Toyota Corolla was driving great all am then all of a sudden it hesitated over and over within 5 minutes going home would that narrow down the 5 reasons to one or 2 reasons?
No, I’m afraid it won’t. You might want to run it by a local mechanic to have that diagnosed.
the information was very helpful. thank you
Thanks for the feedback!
Good day car hesitate and slip. But engine make loud noise when the gear slip. Gear won’t shift to next and can only move slowly. When I press accelerator rpm will go high and car will just move slowly. If i continue pressing the accelerator, not minding the engine noise, the gear will select and I can drive fast up to only 40kmh. The problem will start all over again if I the the gear in park and I want to run again. 00 camry Toyota 5s fe engine a140e gear
That’s a tough one to diagnose without hearing the sound and where it’s coming from. Can you describe the sound in detail?
It’d probably be best to bring your car to a nearby mechanic.
Information was helpful thank u
Thank you for your useful reply.
We often drive our car on a near empty gas tank, which may be responsible for the problems.