Have you noticed your car idles high then drops suddenly? This can be frustrating and may even be a sign of a larger problem with your vehicle.
If not addressed promptly, these issues can lead to unstable car performance, reduced fuel economy, worst misfires, and other problems.
Hence, it is essential to identify and fix the underlying cause of high rpm idling trouble to prevent further damage to your vehicle.
What Causes Car Idles High Then Drops?
It’s normal when your vehicle’s idle fluctuates suddenly, but if it persists, there could be a hidden issue, like vacuum leaks or dirty or malfunctioning idle air control valves.
Other causes include clogged fuel injection systems, or a failure in throttle position or mass air flow sensors, coolant temperature sensors, spark plugs, or oxygen sensors.
Vacuum Leaks
A common cause when a car idles high when first started and then dropping is vacuum leaks.
A faulty vacuum gauge occurs when air enters the engine outside the normal air intake system, rendering the air-to-fuel ratio imbalance.
This leads to a higher idle speed than RPM drop, as the engine compensates for the extra air.
Various issues, including cracked or disconnected hoses, a malfunctioning PCV valve, or a faulty intake manifold gasket, can trigger vacuum hose leaks.
Once the broken vacuum is fixed, or the excess air is burned off, the idle speed drops to normal.
Dirty Or Malfunctioning Idle Air Control Valve
The IAC valve regulates the quantity of air that flows through into the device at idle to manage the car’s idle speed.
Over time, the IAC valve can become clogged with dirt and debris.
It will then malfunction and either not allow enough air to flow through or too much air to pass, resulting in erratic engine revs while idling.
Throttle Position Sensor Failure
A defective throttle position sensor might result in rough idling.
The throttle position sensor monitors the throttle position and relays information to the computer’s memory. It changes the fuel or air mixture to maintain the correct vehicle’s speed.
Suppose the throttle position sensor is malfunctioning or sending incorrect data.
In that case, the engine can idle at a higher-than-normal RPM, then suddenly drop, and you can feel a jerking or surging sensation while driving.
Faulty Coolant Temperature Sensor
The coolant temperature sensor informs the car’s computer about the engine’s temperature.
If the sensor is not working correctly, the computer may not know when the automobile has warmed up and may continue to supply extra fuel, causing the engine revving in idle.
Alternatively, when the sensor is reading a temperature that is too high, the computer may believe the engine is overheating and drop the idle.
Malfunctioning Mass Air Flow Sensor
A defective mass air flow (MAF) sensor can also be a reason for a car revving while idling.
The MAF sensor detects the quantity of air entering the device and transmits that data to the vehicle’s computer.
If the MAF sensor is faulty or dirty, it can send error codes to the computer, and the car receives too much or too little air. Idle issues or a fluctuation in engine RPMs are on the horizon.
You should reset the MAF sensor to this end.
Worn Spark Plugs
Worn spark plugs also explain why a car would idle high, then RPMs drop. Spark plugs are in charge of producing the spark that ignites the gasoline pump in the engine.
Over time, this part can become worn, corroded, or fouled, which can hinder the vehicle’s performance, generating rough idling.
A worn spark plug may not provide enough spark to ignite the fuel properly, ending up with high idling rpm as it tries to back up the lack of power.
Faulty O2 Sensor
The O2 sensor monitors the oxygen level in the car’s exhaust system. This information is then sent to the engine control module, which adjusts the air-fuel mixture accordingly.
If the oxygen sensor malfunctions, it may deliver incorrect readings to the RPM sensor control module, leading to high idling when starting the car and then dropping.
Dirty Fuel Injectors
Fuel injection systems are responsible for delivering the correct amount of fuel into the engine for combustion.
These can get blocked with dirt, debris, or other impurities over time, resulting in poor fuel pump delivery and engine misfires.
Fuel injection failure explains why the car revs while idle and then drops suddenly or stalls.
How To Prevent Car Idles High Then Drops?
If you notice any issues with your car’s idling, bring it to the auto part stores to address error codes.
However, to prevent engine revving at idle from happening, there are several steps you can take:
- Regular maintenance: Proper maintenance of your car’s engine is essential in preventing idling issues. Regularly check and replace air filters, fuel filters, and spark plugs.
- Use high-quality fuel: Always use high-quality fuel in your car to prevent the buildup of deposits and contamination in the fuel system, which is the source of idling issues.
- Drive smoothly: Avoid abrupt acceleration or braking, and maintain a consistent driving speed. This will help prevent unnecessary stress on the device.
- Warm up the engine: Letting your engine warm up for a few minutes before driving can help smooth out the idling process.
- Avoid idling for long periods: If you need to stop longer, turn off the engine instead of letting it idle. This will ward off unnecessary wear and tear on the machine and can also help save fuel.
FAQs
Is It Safe To Drive In High Idling Car?
No. It is generally not recommended to drive in a car with high idling.
This is the recipe for problems such as decreased fuel efficiency, increased emissions, and potential damage to the engine and other components.
Additionally, high idling can force the vehicle to accelerate unexpectedly or decelerate, making driving unsafe in certain situations.
Thus, it is crucial to address the underlying root of the car revving when idle before driving the vehicle to ensure safe and proper functioning.
How Much Does It Cost To Fix Car Idles High?
It depends on the replacement parts. The most common cause is the bad idle air control valve, which costs you anywhere between $200 to $500.
This price already covers the labor cost of $50 to $100.
How Much Is Idling Unusual?
The amount of idling considered unusual depends on the make and model of the car. However, most cars should generally idle between 600 to 1000 RPM (revolutions per minute).
If the car is idling at a significantly higher or lower RPM than this range, it may indicate an issue that needs to be remedied.
It’s best to consult a mechanic or refer to the car’s manual for specific idling recommendations.
Conclusion
When your car idles high then drops unexpectedly, it’s critical to treat the problem as quickly as possible to avoid further engine damage.
Understanding the possible culprits behind this issue and taking appropriate action can keep your vehicle running smoothly and avoid more costly repairs.