Imagine driving long distances or on the highway, but your car won’t go over 30 mph. You try pressing the gas pedal, but the vehicle won’t accelerate as expected.
If this is the case with your car, you’re probably wondering what could be the root cause. Unfortunately, there are many potential reasons, and determining the cause can be challenging. It’s advisable to stop the car to diagnose the cause and resolve the problem.
Anything from the car going into limp mode to faulty sensors and clogged filters might be to blame. Herein, I provide possible reasons your car won’t exceed 30 mph and what you can do to resolve this problem. Let’s dive in!
Answer: Why Your Auto Won’t Exceed 30 Mph
Your car won’t exceed 30 mph due to the following reasons.
- Car going into limp mode
- Faulty fuel injectors
- Blocked fuel filter
- Clogged catalytic converter
- Faulty Mass Air Flow sensor
- Defective throttle position sensor
- Bad spark plugs
- Clogged air filter
The Car Has Gone Into Limp Mode
Limp mode (limp home mode) is a low-power mode that serves as a security and safety feature in modern cars. It activates when the ECU or the TCU detects a problem with the powertrain affecting the vehicle’s performance. Its primary role is to protect the engine from further damage.
If your car has entered limp mode, you’ll notice a sudden loss of power and failure to go over 30 mph. The vehicle may turn on the warning lights and get locked into low gear.
The ECU or TCU may activate your car’s limp mode due to several issues. You’ll need to examine the vehicle to determine the cause. If you have an OBDII scanner, connect it to your car and scan the fault codes. You can also clear all the fault codes with the scanner. Doing this will help you know the root cause and fix it.
After fixing the underlying problem, reset the ECU to help it exit limp mode. Resetting the ECU may also help clear the warning lights.
Faulty Fuel Injectors
The engine’s combustion chamber requires a precise amount of fuel to ignite the air/fuel mix. For a complete combustion to happen, the fuel injector must spray/inject the correct amount of fuel into the chamber.
If your car is experiencing loss of power and acceleration issues, the fuel injectors might be to blame. Over time, dirt and contaminants accumulate in the fuel system and clog the injectors. Blocked or clogged injectors won’t send the required fuel to the chamber.
Also, the injectors can suffer from premature wear or damage and fail to inject sufficient fuel into the chamber. These issues may result in your car not going over 30 mph.
Cleaning dirty injectors with a fuel injector cleaner can help resolve the problem. If this method fails, drive the car to a mechanic to have the injectors cleaned, repaired, or replaced.
Blocked Fuel Filter
A blocked/clogged fuel filter is another possible reason your car won’t go over 30 mph. Like fuel injectors, the fuel filter gets clogged over time due to the accumulation of dirt, debris, and contaminants.
This filter has a fine screen that traps dirt, debris, and rust particles to prevent them from entering the engine. If these particles accumulate on the filter, they may block fuel flow to the engine. Insufficient fuel in the combustion chamber will reduce acceleration, among other issues like starting problems, engine misfires, and stalling.
Checking and replacing the fuel filter is part of your car’s routine maintenance. You fix this problem by removing the blocked filter and installing a new one.
Clogged Catalytic Converter
Cars have a mechanism that prevents the emission of toxic exhaust gasses into the atmosphere. They use the catalytic converter to convert these gasses into environmentally friendly products. For example, the catalytic converter will convert the toxic CO into CO2 and hydrocarbons into water.
The catalytic converter is part of the exhaust system. Over time, this emission control component becomes clogged due to accumulated carbon deposits and unburned fuel. The clogs block the exhaust, restricting the flow of exhaust gasses. These gasses accumulate in the engine and cause acceleration problems.
If your car fails to exceed 30 mph, inspect the catalytic converter for clogs.
Faulty Mass Air Flow Sensor
Your ride needs to determine the amount of fuel required based on the airflow to achieve a complete combustion. This is where the mass air flow (MAF) sensor comes in. It calculates the air mass entering the intake manifold and sends this data to the ECU.
The ECU uses this data to determine the fuel needed to create the correct air-to-fuel mixture. If the MAF sensor is dirty or defective, it may send the wrong information to the ECU. As a result, an improper air/fuel mixture will lead to incomplete combustion.
This issue may trigger several problems, including the car not going over 30 mph.
Cleaning a clogged MAF sensor with an aftermarket cleaner can help fix the problem. However, if you have a damaged sensor, you’ll need to replace it and reset the ECU.
Malfunctioning Throttle Position Sensor
A defective throttle position sensor (TPS) could be the culprit if your car won’t go over 30 mph. This sensor plays a critical role in ensuring there’s a correct air/fuel mixture in the engine. It monitors and measures the position of the throttle valve when you press the gas pedal.
The TPS sends the throttle position data to the ECU. Then, the ECU uses this information to control the amount of air entering the intake manifold. If the TPS is faulty, it may send the wrong data to the ECM, leading to an incorrect air/fuel mixture.
The defective sensor will not measure the position of the throttle. As a result, you’ll notice an engine speed decrease despite pressing the accelerator pedal. You can test the TPS with a multimeter and replace it if it is faulty.
Clogged Air Filter
The air filter ensures the engine receives clean air for combustion. It traps dust, dirt, and debris from the incoming air. This component requires regular cleaning or replacement to ensure efficient airflow.
If you’ve neglected your car’s routine maintenance, dirt and debris can accumulate on this filter and block airflow. A clogged/blocked air filter will cause the engine to run rich, resulting in incomplete combustion. This issue will affect the engine’s efficiency and cause poor acceleration.
So, if your vehicle’s speed doesn’t exceed 30 mph, locate the air filter underneath the hood and inspect it for clogs. You can remove and clean the clogged filter. If it looks excessively clogged or damaged, replace it.
Bad Spark Plugs
Your car’s spark plugs need to be in good condition to provide a spark for igniting the air/fuel mixture. Unfortunately, spark plugs will not last a lifetime in your engine. They get clogged, loose, worn, or blown and fail to create the spark.
A bad spark plug comes with several symptoms, such as engine misfires, rough idling, lack of acceleration, and starting problems. If your car fails to go over 30 mph, you might have one or more faulty plugs.
Remove all the plugs and inspect them for clogs or damage. Use a sandpaper or blow torch to remove hardened clogs on the plugs. Alternatively, you can replace the clogged or defective plugs. Spark plugs are inexpensive, and you can replace them without professional help.
Wrapping Up
Hopefully, I’ve explained one of the reasons your car won’t go over 30 mph. There’s a high chance the ECU has activated limp mode after detecting issues with the powertrain. If the vehicle is not in limp mode but doesn’t exceed 30 mph, there might be several other issues to blame.
Diagnose the problem and fix it to prevent more issues from occurring. A diagnostic tool can help you scan the error codes and know the problems to fix. However, if you can’t troubleshoot the problem, drive or tow the car to an auto repair shop for fixing.