Why is my engine struggling to stay running?
If your engine is struggling to stay running, it could be due to a variety of issues, such as a problem with the fuel system, ignition system, or engine sensors. In this article, we'll explore the common causes of an engine that has difficulty maintaining a steady idle or staying running, and provide some troubleshooting steps to help you identify and resolve the problem.
Fuel System Issues
One of the most common reasons for an engine struggling to stay running is a problem with the fuel system. This could be due to a clogged fuel filter, a faulty fuel pump, or a leak in the fuel lines. A clogged fuel filter can restrict the flow of fuel to the engine, causing it to stall or run rough. To fix this, you'll need to replace the fuel filter. A failing fuel pump may not be able to provide enough fuel pressure to the engine, leading to stalling or difficulty maintaining idle. You can test the fuel pump by checking the fuel pressure at the fuel rail. Fuel leaks can also cause the engine to lose fuel pressure and stall.
Ignition System Problems
Issues with the ignition system can also cause an engine to struggle to stay running. Faulty spark plugs, a problem with the ignition coils, or a malfunctioning ignition module can all lead to misfiring and engine stalling. To diagnose ignition system issues, you can use a multimeter to test the spark plugs and ignition coils, and check for any error codes related to the ignition system.
Engine Sensor Malfunctions
Engine sensors, such as the oxygen sensors, mass airflow sensor, or throttle position sensor, provide important information to the engine control module (ECM) to maintain proper engine operation. If one of these sensors is malfunctioning, it can cause the engine to run poorly and have difficulty staying running. You can use a diagnostic tool to check for any trouble codes related to engine sensors and replace any faulty components.
Troubleshooting Steps
- Check the fuel system for any leaks, clogs, or issues with the fuel pump
- Test the spark plugs and ignition coils for proper operation
- Use a diagnostic tool to check for any trouble codes related to engine sensors
- Inspect the air filter and ensure the engine is getting adequate airflow
- Check for any vacuum leaks that could be causing the engine to run rough
By following these troubleshooting steps, you should be able to identify and resolve the issue causing your engine to struggle to stay running. If the problem persists, it's best to have a professional mechanic diagnose and repair the issue.
What to do if my car starts but won't stay running?
If your car starts but stops immediately, it's likely due to a faulty part that needs to be repaired or replaced, such as a bad battery or alternator or a faulty fuel injector or spark plug. If the car starts and then stalls, see if you can keep it running by applying a bit of throttle when you first start it.
Why is my engine struggling to stay on?
There are multiple reasons why your car could be cutting out, these will generally fall under the following: an electrical issue (faulty sensor or control module), a fuelling issue (blocked fuel filter or bad fuel pump), or a spark issue (faulty ignition coil or bad spark plugs).
How to fix a rough idling engine?
To fix a rough idle, first perform a basic check of the air filter and clean the throttle body and idle air control (IAC) valve, which are common causes of poor idling. If the problem persists, check for vacuum leaks, clean or replace the spark plugs, and ensure the fuel injectors are clean and the fuel filter is in good condition.
This video explains how to clean the throttle body and idle air control valve: 48sChrisFixYouTube · Sep 3, 2020
Initial checks and cleaning
- Check and clean the air filter: A dirty or clogged air filter restricts airflow, causing the engine to run rich and idle poorly.
- Clean the throttle body and IAC valve: Carbon buildup on the throttle plate can cause it to stick. Clean the throttle body with a throttle body cleaner, being careful not to damage electronic components. Some modern cars have the IAC integrated into the throttle body, so you may only need to clean one part.
- Check spark plugs: Worn or contaminated spark plugs can lead to misfires and a rough idle. Check them for damage, corrosion, or oil, and replace them as needed.
Intermediate checks and cleaning
- Inspect for vacuum leaks: Cracked or brittle vacuum hoses can allow unmetered air into the engine, leading to a lean fuel mixture and rough idle. Look for and seal any cracks in hoses or other intake components.
- Clean the fuel injectors: Use a quality fuel injector cleaner additive in your gas tank to help clean deposits. For a more thorough cleaning, injectors may need to be removed and professionally cleaned.
- Check the fuel system: A clogged fuel filter or failing fuel pump can affect the amount of fuel getting to the engine.
This video shows how to identify a vacuum leak in the air intake system: 57sWindows DownYouTube · Mar 29, 2021
Advanced diagnostics
- Use a diagnostic scanner: A scanner can reveal specific error codes, check for misfire history, and show real-time engine data, such as fuel trims, to help pinpoint the problem.
- Perform a compression test: This can help determine if there are internal engine issues, such as worn piston rings or a bad valve, that are causing the rough idle.
You can watch this video to learn how to diagnose a rough idle with a scan tool: 1mBudget MechanicYouTube · Aug 22, 2025
Why won't my car stay running unless my foot is on gas?
A car that starts but won't stay running unless the gas pedal is pressed typically has an issue with the idle air control (IAC) valve, vacuum leaks, or a dirty throttle body. Other common causes include low fuel pressure, a faulty fuel pump, or a clogged fuel filter.
Potential causes
This video explains the causes and solutions for a car that won't stay running: 54sOBD InsightsYouTube · Jan 9, 2024
- Idle Air Control (IAC) Valve: This valve controls the engine's idle speed by regulating airflow. If it's dirty or failing, the engine won't get the correct amount of air at idle and may stall.
- Vacuum Leaks: Leaks in hoses or gaskets can cause unmetered air to enter the engine, disrupting the air-fuel mixture and leading to an unstable idle.
- Dirty Throttle Body: A buildup of carbon on the throttle plate can prevent it from closing properly, interfering with the engine's ability to maintain a steady idle.
- Fuel Delivery Issues: A failing fuel pump or a clogged fuel filter can lead to low fuel pressure. Pressing the gas pedal may temporarily increase pressure, but the engine still won't run properly without a consistent supply.
- Mass Airflow (MAF) Sensor: A dirty or faulty MAF sensor can send incorrect data to the engine's computer about the amount of air entering the engine, causing performance problems.
- Throttle Position Sensor (TPS): A malfunctioning TPS can send incorrect signals about the throttle's position, leading to an improper fuel-air mix and stalling.
What to do
- Clean the throttle body and MAF sensor: You can try cleaning these yourself with specific cleaners to see if that resolves the issue.
- Check for vacuum leaks: Inspect all hoses and connections for cracks or disconnections.
- Test the fuel pump: Have a mechanic check the fuel pressure to ensure it's within the correct range.
- Inspect the IAC valve: If cleaning doesn't help, the IAC valve may need to be replaced.
- Check other components: If the problem persists, consider checking spark plugs and fuel injectors for clogs or other issues.
