Hard Starting Engine – Cold, Hot, Both or just after, adding fuel.

Hard Starting Engine - Cold, Hot, Both or just after, adding fuel.
Hard Starting Engine - Cold, Hot, Both or just after, adding fuel.

So, a hard starting engine, is not a good sign and can be difficult to diagnose.

But, the exact moment in the process of starting; can tell you a tremendous amount, of what may be going on.

In addition, if your car won’t start, it’s important to note what’s happening, when you turn the key. Also, what’s different from the last time it started ok.

Unfortunately, there is no easy solution, that can work for all hard starting engine cases. But, paying attention early, may steer you down the right path, to a easy repair. If the engine takes, more than 4 seconds to start, there is a problem.

There are a number of issues, that can make a car hard to start. Everything from the electrical system, to the fuel system or to the actual starter itself, can be the problem.

But, the number one cause for this problem is, a vacuum leak.

Vacuum Leak
Vacuum Leak

Consequently, I would recommend doing a vacuum test before moving on.

Before, the troubleshooting begins, we must know if there is, a check engine or service engine soon light “ON”.

Always Start By Looking For Any, Diagnostic Trouble Code (DTC)

Your vehicle engine control unit, monitors important emission control systems, through several sensors and actuators to make necessary adjustments. So, when any one of these sensors, deviate from its normal parameters; a diagnostic trouble code, is set in its memory.

Hard Starting Engine
Checking For Diagnostic Trouble Codes

This means, your check engine light (CEL) will come on. However, a fault may come and go. An intermittent fault like this, could set a pending (DTC), without making your (CEL) illuminate. Still, you should scan your computer, for pending codes.

Here’s A List Of The Most Common Faults You Should Look For:

Always Check Sensors, Filters And Vacuum Leaks.

Hard Starting Engine
Automotive Sensors

Mass Air Flow (MAF) Sensor:

  • Over time, dirt or foreign matter, can cover the sensing element, preventing the sensor from operating correctly.
  • Check the sensor, clean it if necessary and make sure to, reinstall the air cleaning assembly properly.
  • So, as to prevent, unmetered air from entering the engine.

Throttle Position Sensor (TPS)

Usually, a bad or failing (TPS) sensor, will trigger the check engine light (CEL). So, scan the computer memory for diagnostic trouble codes (DTCs).

Positive Crankcase Ventilation (PCV) Valve And Connecting Hoses

A stuck open (PCV) valve, can have an adverse effect, on engine starting.

Air filter

If the paper element seems, covered in dirt or clogged, install a new one. If you haven’t replaced it, in more than two years, replace it.

Vacuum leaks

A vacuum leak, will make it hard for the computer to figure out, the correct air-fuel mixture. Trace every vacuum hose looking for rough, soft, hard, or uneven spots, that may indicate, a damaged hose.

Throttle Valve (throttle plate) And Bore

Carbon deposits, in the valve or body can interfere with the valve. Use carburetor cleaner and a shop rag, to remove deposits. NOTE: Some vehicle manufacturers, apply a protective coating to the throttle bore, that makes it hard for sludge to accumulate. So, cleaning the bore, with an aftermarket chemical, may remove this coating.

Idle Air Control (IAC) Solenoid

The solenoid allows extra air to enter the engine at idle, depending on operating conditions. Over time, the valve passages may fill with carbon deposits, that can interfere with its operation. Remove the solenoid and inspect the passages. You can find it, near the throttle body. If necessary, check the solenoid for proper operation.

Engine Coolant Temperature (ECT) Sensor:

The sensor is in charge of reporting, the coolant temperature, at any given moment. The computer uses this information along with information, from other sensors.

Hard Starting Engine
Engine Coolant Temperature (ECT) Sensor

Consequently, adding more fuel to the mixture; when the engine is cold and leaning the mixture, as the engine warms up. Even more, the computer uses information from, (ECT) and other sensors, to adjust ignition timing as needed.

Hard Starting Engine, When Cold

A hard starting engine when cold, is usually associated with, certain components, when they begin to fail or wear out.

Although not exclusive to this condition, the following components, are worth checking:

Check Ignition Components

Bad spark plugs, are blamed for many performance issues. Poor fuel economy, low power, misfiring and, yes, hard starting engine, when cold.

Check Fuel System Components

Lack of necessary fuel system pressure, will make it hard for your engine to start.

Fuel Pressure Regulator
Fuel Pressure Regulator

This may happen on a cold engine, if pressure is slowly leaking or not building appropriately.

Hard Starting Engine, When Hot

Some components or systems that cause starting problems cold, may also cause, problems when hot. So, don’t forget to scan your computer for (DTC)s. Even if the (CEL) hasn’t come on, you may find some pending codes, that can guide you in your diagnostic.

Check Fuel System Components

Automotive Fuel System
Automotive Fuel System

Look for an obstruction to fuel flow or a malfunctioning component, preventing fuel from, properly reaching the engine.

Check Engine Ground Connections

A bad engine ground connection, can work as, an unwanted resistance in a circuit. Once the engine has reached operating temperature, the heat will add some, unwanted resistance to any wire. The same effect can happen from, corrosion dirt or grease around, an electrical connection. A torn, damaged, or oil-contaminated strap connection, can interfere with this current path.

Hard Starting Engine When, Cold or Hot

There are varied reasons why, you may have a hard time starting the engine, when cold or hot:

Starting System And Battery

This is perhaps the most common fault to appear, under this condition. You may notice the starter motor not working as usual or weak. Check your battery first. Then, have the starter motor tested, if necessary. Most auto part stores, will check the starter motor and battery for you.

Vacuum Leaks

The number of vacuum hoses, differ from one engine model to another. But, most have an emissions diagram label, at the front of the engine compartment. Check each of these hoses, for proper connection, damage, wear and uneven spots. To make it easier, trace each hose with your hand. You may need a mirror, to help you inspect some hoses, in difficult to reach places.

Ignition System:

  • Carbon deposits around the plugs’ electrodes.
  • Worn out spark plugs.
Worn Spark Plugs
Worn Spark Plugs
  • Check spark plug wires resistance.
  • Carbon traces around the distributor cap and rotor, if equipped.

Fuel System

Check for a clogging or leaking fuel injector, bad fuel filter, fuel pressure regulator, or faulty fuel pump.

Mechanical Problems:

Carbon buildup, around the intake valves, can also give you problems, during engine start up.

Carbon Buildup Around The Intake Valves
Carbon Buildup Around The Intake Valves

Service the valves with, a decarbonizing chemical, if necessary.

Hard Starting Engine, After Refueling

All (EVAP) systems have, a charcoal canister, that it relies on. The canister has a huge surface area, that is effective in storing vapors from the fuel. If the charcoal canister were to go bad, there would be an array of problems. In addition, to power reduction, fuel odor, more pinging, lower fuel economy, and flooding.

Evaporative Emission Control System (EVAP)

So, most common problems with the (EVAP) system include, faults with the purge valve. The canister purge valve, also commonly referred to as, the purge valve; is an important component of your (EVAP) system. So, this system restricts the fuel vapors created in your fuel tank; from escaping into the atmosphere, by trapping them. When your engine runs at regular speed; the (EVAP) system, slowly allows these vapors to be, released into your engine.

Bad Or Failing Gas Cap

The gas cap, also known as the fuel filler cap, is a simple, but important component. Their purpose is simple, to prevent dirt, debris, and dust from entering the gas tank; as well as providing a reliable seal. The cap also plays an important role in the operation of the vehicle’s, (EVAP) emissions system. The (EVAP) is designed, to capture and reuse fuel vapors from the gas tank. Because, the cap is frequently removed, every time fuel is added, it can wear out.

Purge Valve

The flow of these vapors is controlled, by the canister purge valve. The valve regulates, when and how much of these vapors, enter your engine. The canister purge valve, is electrically operated and is also referred to commonly as, a solenoid. The most common purge valve issues are, when the purge valve is stuck open or closed. Also, it may just not open at the proper time. The symptoms are listed below that may indicate, your canister purge valve is not functioning properly.

Check Engine Light Is On

The first sign of trouble for your canister purge valve is, the check engine light coming on. Consequently, your canister purge valve is controlled by your car’s computer, which allows it to monitor its performance. If your car’s computer detects higher or lower than expected purging, it will illuminate the check engine light. Common error codes include, P0441 and P0446, as well as other (EVAP) codes.

Purge Valve Stuck Closed

Furthermore, if your canister purge valve is not opening properly it may adversely, impact your gas mileage. As a result, you will lose a portion of the fuel, regularly used in burning.

Purge Valve Stuck Open

So, if your canister purge valve is stuck open, it creates a vacuum leak. Simply put, air will be allowed to enter the engine in a quantity that is, not predicted by your computer. This will change the car’s air to fuel ratio and can cause, rough idling as well as, difficulty starting. Therefore, if experienced together, there is a high likelihood of a, failing canister valve. As a result, this enriches the fuel mixture and will likely, foul the spark plugs.


When a hard starting engine condition suddenly appears, the first thing we do is panic. But, remember that your car engine and computer; rely on sensors, actuators, hoses, fluids and electrical systems for proper operation. Finally, once a component that is in need of attention begins to fail; it can cause, other components or systems to fail.