Top 6 Causes of a Car That Won’t Accelerate

Last Updated on March 9, 2021

The symptoms of a car not accelerating like it used to can occur on many high mileage vehicles. A driver might not notice these signs in normal day to day driving but they become abundantly clear when driving up a steep hill or when quickly trying to accelerate into fast moving traffic.

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It is in those situations that drivers will come to notice the obvious slow acceleration and the fact that the engine of their vehicle is struggling to keep up.

Read also: Symptoms of a Faulty Speed Sensor in Your Vehicle

Common Causes of Car That Won’t Properly Accelerate

This is a common problem in high mileage vehicles but there are no serious or immediate concerns regarding major engine problems. Some of the causes are actually minor and should be checked first in order to locate the issue and possibly fix it as well. Here are some of the most common causes:

#1 – Mass Air Flow Sensor Clogged or Malfunctioned

MAF sensor

The mass air flow sensor (or meter) is located and attached to the inlet air cleaner. Since the function of the air flow sensor is to measure air mass that is flowing into air intake, a clogged or bad mass air flow sensor could send the wrong data to the engine ECU for calculating the air fuel mixture.

A very symptom of an air flow meter malfunction is car that won’t accelerate correctly.

#2 – Oxygen Sensor Malfunction

oxygen sensor

An oxygen sensor is device whose function is to monitor the exhaust emissions of the vehicle so that it can analyze the air-fuel ratio going through the engine of that vehicle.

To make a long story short, a car needs a proper amount of fuel in order for the fuel to burn properly in the combustion cylinders so that it may run smoothly and may accelerate as required.

This sensor sends the information about the amount of fuel being used to the computer unit of the engine and if this sensor get damaged, then the engine of that vehicle will have no idea what ratio of air-fuel mixture to use which may result in a fuel rich mixture.

This can cause the slow acceleration of the vehicle even with the accelerator pedal completely pressed making it unreliable when it’s needed.

#3 – Malfunction of TPS

TPS sensor

The basic principle of the throttle position sensor (TPS) is to detect the throttle valve opening angle which is controlled by accelerator pedal. Then the TPS will send this data to the ECU.

If the TPS malfunctions, the engine speed cannot be controlled by the accelerator pedal and engine speed will increase or decrease without any press or depress the pedal.

#4 – Dirty or Clogged Fuel Filter

fuel filter

A dirty or clogged fuel filter is another reason for a car not accelerating like it’s supposed to when required to do so.

With a dirty fuel filter, the engine won’t be getting enough fuel which means that the vehicle won’t be giving the acceleration performance that it should. Replace the fuel filter as soon as possible.

#5 – Clogged or Dirty Air Filters

dirty air filter

Just like a fuel filter provides the engine with the clean fuel, an air filter provides the engine of a vehicle with clean air to be used in the air-fuel mixture which will be sent to the combustion chambers to burn.

If an air filter is clogged, then the engine won’t get the right air-fuel mixture resulting in slow acceleration. Replace the air filter as soon as possible.

#6 – Timing Belt

bad timing belt

This component is as it sounds. The timing belt is something like a VIP in the list key of components of an engine. If this belt is off even by 1 tooth, it may cause some pretty notable acceleration problems.

However the list of causes of poor acceleration does not end here. Other culprits behind slow acceleration may include a slipping clutch, the transmission system itself, or an unexpected or unrelated problem which may surprise even veteran mechanics.

If you’re not comfortable troubleshooting a car that won’t accelerate, I recommend taking the vehicle to a reliable mechanic and let him give it a full checkup. This will allow him to properly diagnose the issue and recommend a suggested fix.

 

349 thoughts on “Top 6 Causes of a Car That Won’t Accelerate”

  1. 2009 model, Mazda 3 car in UAE. After one hour running the car suddenly not taking speed and this happened twice in summer peak time. Mechanic checked and told no issue found.

    Reply
  2. Hi, my car Honda accord 2007 189k miles. Recently, the car can’t accelerate after stopping at the intersection. At that moment, the normal light and several other lights appear on the dashboard but the engine doesn’t run at all. I press the pedal but there is no sound, like completely shut down already but still has light. When I shut down the car and start the engine again, the car works normally. Is this cause by the alternator or anything else. Hope to get help from experts from you guys. Thank you!

    Reply
      • Al the lights like when I first turn the key ignited, but then I shut down the car and start it again, it worked like normal so I’m not sure if a part of my car failing or not. I heard that could be caused by the alternator. Have you heard about this situation happening on old cars?

        Reply
        • When you first turn the key, it’s normal for all lights to illuminate. This is a systems check to let you know that all lamps are working as expected. Is this what you’re referring to?

    • My son ran the front tire off and when I cranked it up to leave it sounded bad and it would not run but 5miles per hour

      Reply
  3. hello.this is also the prblm of my car.so hard to reach 80 to 100kph.maybe i need to bring the car to the shop to avoid more problem

    Reply
  4. 2009 Nissan Altima with 125k miles
    After constant driving (an hour and half solid), the car will not accelerate when given gas. The RPM’s will not rev as more gas is given either. Only happens when car is taken on a small road trip. Transmission was replaced over a year ago.

    Reply
    • You’ll have to do some diagnostic work to narrow down the problem, it could be anything. If you are not comfortable doing that you will probably have to bring it to a mechanic to get the issue fixed.

      Reply
  5. Hi Grayson –
    I have 2009 Altima and have experienced same issue. I’ve taken it to mechanic – nothing found. I’m afraid to drive it.

    Reply
    • KH, Grayson’s description left a lot to interpretation, and it will take a bit of troubleshooting to find the cause of both issues. They may even be different issues. I suggest you bring your vehicle to a different local mechanic and pay a small amount for a diagnostic service to help you find the problem. Ask around and see if you can figure out which shop does the best diagnostics.

      Alternatively you can try searching Altima forums to see if there is a common resolution for this type of issue.

      Reply
  6. 2011 toyota camry base 365k miles. All original stuff. Had a few times doing tune up, the usual tune up stuff like oil change, spark plug changing and that’s it. A sealed trannie and was told it was lifetime and no need to change trannie oil. I went ahead and did a drain and flush just last week. Took 2.5 quarts out only. Going to do a coil pack and spark plug this weekend. Last tune up was at 40k miles ago.

    Symptoms: Lack of power and when gear shifted 3 and 4, it vibrates for a bit. Drives ok to 65 and 70 mph on the highway ok but I have hills here in northern california. It can only go 50 mph and I’m not pushing it either. At first, I pushed it to 60mph and it rattles while rpm is at 2000 and it goes up and down, up and down with the rattling vibration, similar to the 3rd and 4th gear problem.

    This is the reason why I thought it was the trannie so I did a drain and fill and still no help. Just the other day, I changed the air filter and performance was a little better, the knocking on 3rd and 4th was lesser or maybe I went easy on the acceleration cuz I don’t want for the knock to be too hard on the trannie while in gear switching. I’m fixing it on the least amount of money first and go from there. The next step if changing out the coil and plug is to change the fuel filter. I did added them fuel system cleaner into my gas tank, in hoping to clear out the fuel injector if it is clogged. All these were done just recently and like I said, I got a gifted car that I drove like a race car, daily commuter to work 2 hours each way and passing cars and what not. I don’t even take care of it, just the basic changing out the engine oil every 7K miles on fully synthetic oil.

    i hope changing out the coil and plug will solve my problem and will continue to ride her till the next problem pops up. I need her to last till 2022 for me so I can replace her with a brand new vehicle. Thanks for the article, it was a big help in understanding the lack of power to the car.

    Reply
    • Glad the article helped you out. Was the problem there before you changed the transmission fluid? After the fluid change, did you check to make sure the transmission fluid level was correct? Do you experience the problem in every gear, or just 3rd and 4th?

      Reply
      • Well you know, like any other person who just pump gas and drive their vehicle without doing any major maintenance cuz you know, if it is not broken then why fix it. Problem came from pumping chevron gas station at a station somewhere up there in the high elevation mountain. My car first taste of different fuel additive from chevron. 3rd and 4th gear vibrates while shifting gears and usually at 2000 rpm is when it shifted. Then 5th to 6th gear seems ok driving hwy speed of 65 and 70mph. Uphill is when it lacks the power like it is still stuck in 6th gear with rpm at 1500. The drain and fill was done by the toyota dealership so I’m sure they did a good job at giving me proper fill. I mean I know how to do it too by using an ir gun to level out the oil method. I only went to the dealership cuz they do a courtesy X points inspection and gave me a list of results. Air filter was on there, I already did that and it was dirty. Fuel filter was on there so I’m definitely gonna take care of it next. I have not done a smoke test to see if there is any air leak. Thank you sean for that article I read. The dealership paper work did not list any plug or coil but since my car is old and when I did the spark plug change, one of the coil is red/orange oxidized coloration so perhaps that one is the bad one. Since my car is old with high mileage, I might as well change all 4 with 4 new plugs to complete the set. Was gonna do the fuel pump with the fuel filter but after the $1000 quote, I’ll just do the fuel filter for $200. I think these parts are in my fuel tank so I’m not gonna do it myself. No check engine light so my odb 2 reader shows nothing. What indicator I noticed about a month ago was the alternator light goes blinking. After that driving session, it stopped showing.

        At 366k, I only did 4 tune ups with the basic plugs, air filter, oil change and that’s it. oil change with synthetic and filter every 7,000 miles. Everything else is total neglect on my part but at the toyota dealership, when they did the x points inspection, looks like they topped off my fluids. Power steering, brake fluids, engine oil. Payed $200 bux though but it is better than giving it to them lube place where they hire kids to do their services at $170.

        Like I said before, I’m working on what is affordable to fix first and go on from there. I think I remembered you saying that sean and it pays to read your articles. I think it is the fuel pump is the culprit but at $800, I’m still debating if I should fix and ride her for another 100k or just buy another vehicle but I kind of wanting to drive her till 2022 when my hybrid truck comes out and I’ll just buy that new ride instead. For the time being, I just need to care for her just enough so she can last till next year. There are other components that can also be a factor like o2 sensor but usually with that, my check engine light would of gone off by now and the odb reader will pick that up. Hopefully I can find a solution so that others may find it helpful and they too can solve their own car problems. Thanks for everything so far Sean.

        Reply
        • Gotta give an update so others may learn to solve their own problems. I remembered when I was doing the coil and plugs, I disconnected the battery terminal so when it was done, the car started but can not idle. I then did the relearning system because the ECU need to remember the new set of plugs and will remember the new idle. A day goes by, idle bad again. Starts up fine but no idle. Went and got me two bottles, an MAF cleaner and a throttle body cleaner. Cleaned them both out for the very first time in 10 years and 366k miles later. Well what do you know? It started up just fine and even driving gave me a little bit more horsepower at the stop and go. However, driving up the hill is still a struggle. Still no check engine light so I can not pull any coding. Oh and once you clean out your throttle body, the check engine light goes on but them codes are for the MAF. I cleared it with my odb. Now with going up the hill not having the horsepower, it could be the fuel pump. My car has no fuel filter but perhaps it is embedded with the fuel pump. Well the fuel pump has a sensor right? If it goes bad, my check engine light would go on and say something like low pressure. No light. Plus if fuel pump is out, I wouldn’t be able to start the engine and while driving, it would die right? Not happen yet (knock on wood). So I’m thinking it is the trannie. Shift solenoid perhaps. I can go flat 65 to 75mph ok but once up that hill, I don’t hear a gear change and mph drops to 50. I know if I push harder to get a switch, my rpm would jump up and down at the 2000 rpm and the car will shakes like hell. This lead me to think that the gear was at 6th while driving flat and when up them hills, it got stuck and can not downshift.

          I’m at the crossroad of paying the mechanic his diagnostic fees to know for sure and fixing it will cost me a hefty penny. Perhaps I’ll just use that 2011 camry for non mountain driving and city driving only and take that money and buy another car because I do need another reliable car for the daily commute of 2 hours each way and 2 high mountains. I’m not too sure if I should bring it to a mechanic or a trannie specialist. Without a code, I just don’t know.

        • If you know a good local mechanic, I would bring the car to him and pay the small diagnostic fee. It’s well worth it if he knows what he’s doing, it’ll save you both time and money in the long run.

        • 2011 camry 367k miles, all stock and only tune up (plug, air filter, oil change) were done regularly. Already cleaned throttle body and maf sensor and had trannie drain and filled. Everything else is on borrowed time (starter, alternator, fuel filter, fuel pump, shift selinoid, cat converter, fuel injector… ect. ect.

          Took her to a local mechanic shop. Gave descriptions of what is the causal. 3rd and 4th gear has hesitation when changing gears. Up hill climbing can only do 50mph. ONce over the hill or on the flat, can do 65 to 70mph or more like normal to keep up with traffic.

          So the mechanic guy took the car for a joy ride. I saw him did that much. When he returned, he lifted my car up to see the bottom. Not too sure what he did to test or not test since I left the scene and came back 1 hour later. Pricing was $90 for diagnostic. So the results came back. I can not believe it but he said everything that I already thought I knew. His sheet of paper to fill out the report was empty. Could not repeat the problem since no check engine light was on. I’m like, you don’t need the check engine light to diagnose the air, fire or gas issues. I don’t have the equipment to test it thus why I’m bringing it to the professional in the first place. He then said he can not make recommendation or playing guessing game and have the customer getting mad when the problem still persist. Maybe they are just toying with me just to make a buck. I dunno.

          Maybe it is my fault for not asking what is a diagnostic and perhaps I can use what I learned from sean and explain it to them that I do know something about cars and don’t take me on for a joy ride.

          I then added another bottle of engine treatment cleaner and I’m getting better performance on the stop and go. The hesitation on 3rd and 4th gear is unnoticeable or maybe it is the way I drive as I am taking it easy with my car now. As soon as I hear the transmission on 3rd and 4th engages, I lay off the gas and doing so will not cause a shifting hesitation. I also do know that there are other potential problems like a bad cat which can show symptoms that mirrors a bad trannie. If I have a bad cat, I would have a hard time starting the car or have a max speed of lets say 40mph and/or the check engine light would go on with code p0420. Air not flowing out the tail end which pushes back the air into the engine to causes an overheat issue with the radiator or blown head gasket.

          My next step is probably gonna be taking my car to a muffler place and ask if they can check if enough air is coming out of my cat and if I needed a new cat, I will buy one from them. Free diagnostic right?

          If problem still exist, trannie shop here I come and maybe they can see if the torque convertor or shift selinoid needs to be replace.

  7. Hi. I have a 2015 automatic Honda Brio. The problem is whenever I get to an intersection it sometimes doesn’t accelerate when i try take off. Sometimes i have to press the breaks hard and accelerate quickly then it will move.However if it’s moving and I let go of the accelerator when I do press accelerator it picks up immediately. Hasn’t really lost any power. This only happens when i stop and try taking off.

    Reply
    • I’m not sure. Sounds like it may be a transmission issue that’s causing it to struggle when launching from a standstill, but it would be best to have it inspected so you have a better idea of what the problem is.

      Reply
  8. Hi. I have a 2007 toyota corolla LE. The problem is whenever I get to an intersection it sometimes doesn’t accelerate when i try take off. Sometimes i have to press the breaks hard and accelerate quickly then it will move.However if it’s moving and I let go of the accelerator when I do press accelerator it picks up immediately. Hasn’t really lost any power. This only happens when i stop and try taking off.

    Reply
    • Not sure, it could be any number of things. Is the check engine light on, and do you have any stored codes? When was the last time the spark plugs were changed?

      Reply

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