Why My Car Won’t Go Faster Than 30 Mph?

When I was on a long drive, my car goes at top speed for nearly 30 mins. Suddenly I notice that the speed of my car goes down. after that my car won’t go faster than 30 mph. Cars are the perfect driving material to go long miles. Higher the car variant higher the speed. The car starts accelerating when you put on feet on the gas pedal. Sometimes even when you push the gas pedal with a stronger force your car goes slower.

"car won't go faster"

It is a frequent issue happening in high-mileage cars. Several minor issues accumulate to reduce the acceleration in the vehicle. Here we have provided the potential reasons for the minimal acceleration of the car.

What Are The Reasons That Your Car Won’t Go Faster Than 30 Mph?

The potential causes may be a minor issues. It may be difficult for a driver to feel the symptoms while driving on a flat road. When he drives on the inclined road he may feel that the car is struggling to accelerate. At that time you may find one or more of mentioned reasons would stop the car from accelerating more than 30 mph.

1. Malfunctioning Of Mass Air Flow Sensor

The Mass Air Flow sensor regulates the Correct proportion of air to the air-fuel ratio mixture. It is fixed to the inlet air cleaner. It won’t send the correct reading or the correct quantity of air for the air-fuel mixture when it is clogged.

clogged mass air flow filter

The quantity of air in the air-fuel ratio may be higher or lower than the actual quantity. This is because of the malfunctioning of the Mass Air Flowmeter. This may be one of the reasons your car won’t go faster than 30mph.

2. Malfunctioning Of Oxygen Sensor

The oxygen sensor measures the exhaust level and regulates the air-fuel ratio before going into the engine’s ignition. The oxygen sensor collects information about the quantity of fuel going through the engine and transfers it to the Electronic control unit (ECU).

Then ECU analyzes whether is the appropriate fuel mixture. The oxygen sensor doesn’t send the information to ECU when it has malfunctioned. ECU uses a larger quantity of fuel due to insufficient information which results in a fuel-rich mixture.

This won’t allow your car to accelerate properly. Hence your car won’t go faster than 30 mph.

3. Malfunctioning Of Throttle Position Sensor

The throttle Position Sensor monitors the opening of the throttle valve position. Ignition of the engine and pumping of fuel into the engine depends on the input of the throttle position sensor. ECU does this process after receiving the input signal.

malfunctioning of throttle positioning valve

Also, the opening of the throttle valve depends on the accelerator pedal. Malfunctioning of throttle position sensor significantly affects the acceleration. This also accounts for your car acceleration not getting over 30 mph.

4. Clogging Of Fuel Filter

The fuel filter is used to prevent the engine from getting damaged. The screen in the filter removes the dirt, dust particles, debris, and tiny rust particles. If any of them enters the engine, it makes the engine wear and tears up in a short period.

An appropriate amount of fuel can’t be provided to the engine due to the clogging of the fuel filter. This won’t allow your car to accelerate properly.

5. Clogging Of Air Filters

The operation of air filters is the same as that of fuel filters. The screen present in the air filter filters the entry of dust and dirt particles into the air. Impure air in the air-fuel mixture will make the combustion process worse. Leading to the damage to the engine.

Clogging of air filters would also lead to a rich fuel mixture. This decreases the efficiency of the engine. Hence your car won’t accelerate properly. Replace the air and the fuel filter before they clogged completely.

6. Damage To Timing Belt

The usage of the timing belt is to keep the engine in running condition. Its work is to ensure the rotation of the crankshaft and camshaft. The vehicle’s piston and valves will operate correctly if both of them run in a proper condition.

timing belt

The timing belt consists of teeth in its structure. It will not work properly if one of the teeth got damaged. This will certainly affect the acceleration of the car. Hence your car won’t go faster than 30 mph

7. Leakage Of Fuel

Fuel injectors are used to deliver the fuel to the engine. It could deliver the appropriate level of fuel to the engine. If the fuel pump pumps the fuel to the injector. The defective fuel pump will lead to a shortage of fuel for the injectors.

car won't go faster

Also, the leakage of fuel leads to a shortage of fuel for injectors. The leakage of fuel in the vacuum system significantly affects the performance of the engine. All of these account for the slower acceleration.

8. Clogging Of Catalytic Converter

The catalytic converter reduces the toxic gases coming out of the engine. The clogging of the catalytic converter leads to the deposition of gases into the engine. This will drastically reduce the acceleration of your car.

9. Failure Of Clutch

The speed of the vehicle changes according to acceleration and deceleration. It depends upon the movement of the clutch. If the clutch got damaged it can’t properly handle the transmission fluid.

"car won't go faster"

The failure of the clutch or the lowering level of transmission fluid would lead to slower acceleration.

10. Failure Of Spark Plugs

The spark plug is responsible for producing the spark used for the ignition of the engine. Spark hitting the cylinder at the wrong time leads to nothing. In turn, several misfires occur due to spark plug and ignition coil.

failure of spark plug

Other than the mentioned causes there are some other culprits like fully or partially pressed emergency, block in the gas pedal, and running the vehicle with an empty fuel tank.

For What Reason Is My Vehicle Slacking When I Press Gas?

A car may lag while speeding up or while driving up a slope and may have a powerless fuel pump. Fuel injectors may get messy after some time and not have the option to give as much fuel to the cylinder as is required. Filthy fuel injectors may make the motor run lean which will cause lagging while speeding up.

Can Spark Plugs Cause Lagging In The Car?

Hard start, lagging and poor speed increase are the basic symptoms of a poor spark plug. On the off chance, that one or more spark plugs are defective, they will experience difficulty in making the spark that causes the starting process in your car.

How To Increase The Car’s Acceleration?

The car’s acceleration can be increased by rectifying the damaged parts.

  • Replace the malfunctioned Mass Air Flow sensor.
  • Insert a new oxygen sensor in the place of the damaged one.
  • Check and replace the throttle position sensor.
  • Remove the dirt from the air filters.
  • Clean the fuel filters.
  • Inspect the timing belt and replace it with a new one.
  • Check for the leakage of fuel. And fix the leakage area.
  • Inspect the working efficiency of the catalytic converter.

You don’t need to replace all the mentioned parts. Replace only if it gets damaged.


Thus clogging of air filters fuel filters damaging the timing belt, malfunctioning of TPS and oxygen sensor, failure of spark plugs, leakage of fuel, and failure of clutch accounts for the cause that your car won’t go faster than 30 mph.

Car won't go faster

Driving with these symptoms is not bad as it was in the initial stage. Suppose you can’t able to find the symptoms and are unable to diagnose them. Don’t hesitate to get your car to the auto-garage. They will analyze all your symptoms with much less effort. Hereby we have concluded Why your car won’t go faster than 30 mph. If any queries, kindly comment down below.

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