What Should Be The RPM of A Car When Starting It?

Almost all average cars with a smaller engine have 680-900 RPM while the cars with larger engines have only 500-600 RPM when you park the car. However, to know the exact RPM of each car at idle you can go through the car manuals. Normal RPM at idle is a sign of comfort and the absence of jumps or ups and downs.

The engine idle can also show variations when the car AC is on or off. However, it becomes normal once the temperature reaches its optimum level. If you are experiencing any ups and downs or the car idling rough when the car is in parking, it is an indication of some kind of trouble or error with your vehicle engine. Idle RPM can be controlled electronically or manually depending on the type and model of the vehicle.

To go further, we first need to understand what a car’s RPM is and its function:

What is a Car RPM at Idle?

The word RPM stands for revolutions per minute while the spinning of the vehicle’s crankshafts within the car engine is described as revolutions. The value of RPM depends on the turning speed of the vehicle engine. It’s directly proportional to it and increases or decreases with the changes in car engines’ turning speed. However, running the vehicle at a higher speed but in a lower gear will result in a lower RPM.

To indicate the normal RPM, most cars have a gauge on their dashboard. They usually indicate 1000 as 10,000 which means that the 1 becomes equal to 1000. Any change in the ignition regularity, vacuum lines, and the air that enters the engine can cause your vehicle to idle roughly but drive smoothly. It can result in unregulated explosions.

What are the Causes of a Rough Running Car?

To deal with the problem of rough-running car adequately, knowing the reasons or causes of the problem is highly crucial. The reason is that repair or treatment selection depends on the location and strength of the damage. Sometimes it can be fixed by simply cleaning or repairing the affected tools while sometimes it requires replacement.

Some major reasons that can cause rough running of a car are:

Clogged Fuel Injectors

One of the major reasons behind car sputtering when idle is the clogged or faulty fuel injectors and damaged fuel system. When they are clogged with dirt or other materials they start leaking fuel. When this fuel burns on the engine, it causes black smoke and higher RPM.

Clogged Fuel Injectors
Photo by: Greg Myers

Vacuum Leakage

Another reason for a rough-running car is vacuum leakage. Car engines have multiple vacuum hoses that help them to work smoothly. When these hoses are worn out, damaged, or start leaking, it causes rough idle. The reason is that they cause lean or mixing of air and fuel.

vehicle engine

EGR Valve Fouled with Carbon

This emission control device is responsible for controlling exhaust gas. When it is damaged or fouled with carbon, it fails to perform its function and causes rough running or RPM fluctuation when driving.

Faulty Carburetor

They are usually present in old and long-distance traveling vehicles. When the shaft present on the base of the carburetor becomes clogged, starts leaking, or wears out, then they start producing the signature black smoke which causes rough running.

car carburetor

Dirty Spark Plugs

These are the most crucial parts of the car ignition system. When they are damaged or worn out, they start causing issues to the engine. It results in rough idle or running of the vehicle.

Car Spark Plug
Photo: Nazly Ahmed

Blocked Air Filter

Another reason car idles rough is the clogged or worn-out air filter. It is crucial for the effective working of the ignition system as it stops dirt and other contaminants from going to the engine. When they become clogged they fail to filter air and even pass sufficient air to the engine.

Another reason car idles rough is the clogged or worn-out air filter

Bad PCV Valve

PCV valves if the engine is responsible for sending back the partially burned glasses to the engine for complete burning. When they are clogged with dirt or slug, they fail to perform their function and start producing smoke. It can even cause an engine fire.

Faulty Oxygen Sensor

It is present in the exhaust system and works continuously to monitor the amount of oxygen delivered to the engine. When they are clogged with carbon, dust, or another slug, they start sending wrong information to the computer data. It causes unbalancing of air and fuel mixture that leads to rough running.

oxygen Sensor

How To Fix a Rough Running Car?

Everyone desires to enjoy a smooth ride with normal RPM at idle after starting the car. However, a constant increase in RPM can cause rough running or car jerks when accelerating. It could happen due to one reason or the combined effects of multiple reasons. Fixing the issue of a rough-running engine right after spotting it is the best way to protect it from further damage.

Some common approaches that can help you to fix this issue are listed here;

Perform Regular Checkup and Maintenance

The best way to protect the engine from sputtering at idle is through regular checkups and maintenance. You can hire the services of a professional mechanic to detect faults and repair them before they become worse.

Vehicle checkup

Know The Cause of Rough Running Car

Another effective approach to fix the issue of RPMs going up and down when accelerating is careful inspection and identification of the main reason or problem. For example, black smoke from the exhaust is a sign of faulty PCV valves and vacuum leakage. It will help you to choose the right treatment.

Repair or Fix the Damages

The best and immediate solution that can help you to cope with a rough running engine is repairing the faulty parts or fixing the damage. However, it’s a temporary solution and costs you massive damages or money loss.

Replace The Defective Parts

The most reliable and permanent solution to stop rough running is replacing the defective and older parts with new and latest ones. Though it’s quite expensive, it will provide you with a permanent solution and smooth riding.


Why is my RPM so High When I Drive?

Many factors cause high RPM when starting a vehicle. From bad fuel injectors to vacuum leaking and faulty carburetors to clogged valves or filters, all are responsible for this problem. They cause a lean or mixing of air and fuel that results in higher RPM when driving.

Why does my Car Idle High?

The reasons or causes of this problem vary from situation to situation. For example, if you are witnessing white smoke production with rough running then it’s because of a blown head gasket or if car exhaust is emitting black smoke then the reason is faulty valves, air filter, and leakage. The best way to detect the exact cause is to hire a professional mechanic.

What Should RPM Be When Starting a Car?

The ideal RPM at idle is 700-900 for small-engine cars and 500-600 RPM for heavy-engine cars.

Experiencing higher RPM when starting the car is not a problem because it happens when the engine remains in rest mode for a long duration. Once the engine reaches the right temperature the RPM becomes normal. If it remains high even after reaching optimum temperature then it’s a sign of faulty or damaged engine parts.


Idling RPM plays a major role in the roughness and smoothness of driving. Therefore, keeping an average of 900-1200 RPM is highly crucial to enjoying a comfortable ride. However, it can be higher than 1500 RPM when starting the vehicle after one day or night. You can use this guide to understand the causes of higher RPM or rough driving and all possible ways to fix it.

Performing regular maintenance checks and sending the car for service to a professional mechanic can help you to avoid this issue.

Last Updated on February 10, 2023 by admin

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