Car Hesitates When Accelerating At Low Speed: Troubleshooting Guide

Why Car Hesitates When Accelerating At Low Speed

There are many possible reasons your car may not accelerate as quickly or smoothly as it should at low speeds. As we mentioned the reasons before, let’s know them in-depth to understand the reasons well.

1. Clogged Air or Fuel Filter

When the air filter is dirty or clogged, it restricts the air supply to the engine, preventing optimal combustion. Similarly, a clogged fuel filter usually robs the engine of fuel, resulting in a lean fuel condition.

Without enough air and fuel supply, the engine cannot generate sufficient power needed to accelerate the car. This may cause a delay in acceleration when stepping on the gas.

How To Diagnose and Fix?

The only way to tell if it is a clogged air or fuel filter that is causing the acceleration problems is through visual inspection. Pop the hood and check the air filter for debris and dirt build-up. Also, inspect the fuel filter screen for debris.

After the diagnosis, you can clean or replace the air filter to fix the problem. Here is how to go about it:

• Step 1: Open the hood and remove the air filter located near the top of the engine.
• Step 2: Vacuum the filter on both sides for at least 2 minutes.
• Step 3: If it is exceedingly dirty, wash the filter in a bucket of clean water and a small dish or laundry detergent. Just swirl it around.
• Step 4: Rinse the filter under running water and leave it to dry before reinstalling it.
• Step 5: If the filter has excessive dirt or is cracked, install a new one.

If it is the fuel filter that is clogged, here is how to replace it:

• Step 1: Disconnect the fuel pump fuse or relay and run your car until it runs out of fuel. This is to relieve the fuel pressure.
• Step 2: Lift the car off the ground.
• Step 3: Locate the filter near the fuel tank.
• Step 4: Put a drip pan underneath the filter to hold any oil that spills.
• Step 5: Detach the fuel lines from the fuel filter. Then, unfasten the clogged filter from its mounting bracket.
• Step 6: Mount the new filter in reverse sequence.

2. Dirty or Damaged Fuel Injectors

Fuel injectors deliver fuel directly to the internal combustion engine. When the injectors become dirty or damaged, this usually affects their ability to supply the right fuel amounts for the combustion.

As a result, the engine cannot generate sufficient power to take off quickly at low speeds.

How To Diagnose and Fix?

Apart from using a mechanic’s stethoscope, you can diagnose faulty injectors using a multimeter. You simply check for open or short circuits by measuring the injector’s resistance.

If the fuel injectors are dirty, you simply need to clean them. You can do this by adding chemical cleaners to the fuel tank and driving your car to allow the cleaner to work. Alternatively, you could use fuel additives.

But if the injectors are damaged, you must replace them. Here are step-by-step instructions:

• Step 1: Disconnect your car battery, the negative terminal first, followed by the positive one.
• Step 2: Depressurize the fuel system by disconnecting the fuel pump relay or fuse. Then, start the engine.
• Step 3: Turn off the engine and let it cool. Then, remove the fuel rail to access the injectors.
• Step 4: Remove all the damaged injectors and install the new ones in reverse order.

3. Faulty Fuel Pump

A fuel pump delivers gas into the engine from the tank via the fuel system, allowing your car to run smoothly. If the pump becomes faulty, it can throw the fuel-to-air ratio off balance due to pressure loss.

As a result, the engine cylinders will be starved of gasoline, making your car hesitate while accelerating from a stop.

How to Diagnose and Fix?

To diagnose a faulty pump, listen for a loud whining noise coming from the gas tank. Alternatively, use a fuel pressure gauge to check for pressure in the fuel lines. If the reading is zero, the pump is dead, and you must replace it. This is how you do it:

• Step 1: Relieve pressure from the fuel system.
• Step 2: Drain as much fuel from the gas tank.
• Step 3: Unhook the electrical connection and filler tube hose from the pump.
• Step 4: Remove the fuel tank.
• Step 5: Detach the fuel lines. Then, take out the fuel pump from the tank.
• Step 6: Mount the new pump in a reverse sequence.

4. Defective Spark Plugs

Spark plugs supply an electric spark that ignites the fuel/air mixture, ensuring your car starts up. If they become defective or worn out, they cannot emit the spark and rightly ignite the fuel. Following this, your car will struggle to accelerate at slow speeds.

How To Diagnose and Fix?

Remove the spark plugs and inspect them for stubborn deposits or cracked porcelain. If these conditions exist, you must replace the defective plugs by following these steps:

• Step 1: Unhook the negative battery cable.
• Step 2: Disconnect the spark plug wires.
• Step 3: Unscrew the defective spark plug from the engine.
• Step 4: Install the new plug in the same manner.

5. Vacuum Leak

A vacuum leak in the intake manifold can cause your car to run lean, leading to poor acceleration. This happens when the vacuum hoses are cracked or worn out, causing them to release excess air into the engine. And when this happens, the engine gets starved of fuel.

How To Diagnose and Fix?

To diagnose a vacuum leak, spray some soapy water on the areas you suspect a leak while the engine is running. If the water gets sucked, that’s where the leak is. 

However, the best solution depends entirely on the cause of the vacuum leak. Below are the possible fixes:

• Replace any leaking vacuum hoses
• Install a new intake manifold gasket
• Repair or replace the brake booster
• Replace the exhaust gas recirculation valve
• Seal the leak using epoxy or silicone sealer
• Install a new intake manifold if severely damaged

6. Faulty Mass Airflow, Oxygen, or Throttle Position Sensors

The mass airflow (MAF), oxygen, and throttle position sensors control the amount of air that enters the engine. If these sensors are faulty, they won’t send the correct information to the ECU. Consequently, too much air and little fuel will be pushed into the combustion chamber, causing sluggish acceleration at low speeds.

How To Diagnose and Fix?

To diagnose a faulty MAF sensor, check for black exhaust or use an OBD-II scanner to check for trouble codes like P0101.

Similarly, you can diagnose a bad oxygen or throttle position sensor using an OBD-II scanner. For a faulty oxygen sensor, you will get trouble codes like P0171 or P0174. On the other hand, a bad throttle position sensor will trigger codes like P0122.

If the MAF sensor is the problem, you can clean it with an electrical cleaner or replace it. As for the oxygen sensor, the only viable solution is to replace it if it’s faulty.

However, if the issue is with the throttle position sensor (TPS), you can have it reprogrammed by a professional mechanic. Another solution is to replace it by following these steps:

• Step 1: Unhook the negative battery cable.
• Step 2: Locate the sensor on the throttle body between the air filter and the engine’s intake manifold.
• Step 3: Disconnect the wiring harness connector from the sensor.
• Step 4: Unscrew the mounting screws on the sensor and pull it out.
• Step 5: Install the new TPS onto the throttle body in reverse order.

You can also watch the video below for a more detailed explanation of how to replace the TPS: