7 Reasons Your Car RPMs Out of Control
Few things are more frightening to drivers than a vehicle problem that seems to occur on its own. When your car’s RPMs suddenly increase for no apparent reason, it’s a sign of potential danger and will have you wondering if it’s safe to drive.
Learn the main reasons why your engine may rev out of control and how to identify and fix them.
What is “revving”? The term “revving” is used to describe any instance where a vehicle’s engine speed increases, either automatically or in response to pressure on the accelerator pedal. As expected, the howling occurs when accelerating while driving to reach a target speed. On the other hand, the howling can also occur when you press the accelerator pedal in park or idle position, when the vehicle is stationary.
If you drive a car with a powerful V8 engine, you have almost certainly revved the engine at some point to hear that powerful, throaty sound. If not, you should do this. And yes, you can rev a small 4-cylinder engine. However, don’t expect the same reaction.
As mentioned above, feedback means that your vehicle’s engine speed increases. This speed is measured in revolutions per minute (RPM). Your vehicle’s tachometer built into the dash will always show you how fast your engine is running. Alternatively, you can listen for the engine speed to increase.
Whistling under normal circumstances is a natural part of engine operation and is to be expected. The deeper you press the gas pedal in your car, the more noticeable and longer the whistling will feel. However, whistling that occurs randomly or for seemingly no reason is something else entirely and can be a cause for concern.
What Causes Your Car to Whinny on Its Own There are several possible causes for an unexpected or unanticipated engine whine, and each one must be considered when diagnosing this type of problem. Understanding the cause of random engine whine is the first step to resolving this alarming condition. Here are some of the most common causes of unexpected engine revs:
1) Vacuum Leaks
Under normal operating conditions, the amount of air entering the engine’s intake tract for combustion is limited by the action of the throttle valve/plate. However, vacuum leaks circumvent this design assumption by allowing unmetered air into the same space. This often results in a significant increase in speed.
How to Fix the Problem: The only way to solve engine revs caused by one or more vacuum leaks is to identify and repair the vacuum leak in question. This can be done by visual inspection or with the use of a smoke machine.
2) Sensor Failure
Modern vehicles are equipped with a variety of sensors, all of which are designed to increase operational efficiency. If some of these sensors fail, it can cause noticeable fluctuations in speed. Some of the most notable of these sensors include the mass airflow sensor, coolant temperature sensor, and throttle position sensor.
How to fix the problem: To fix sensor-related throttle fluctuations, you will need to replace the sensor in question. Diagnosing a sensor failure typically involves reading trouble codes, performing a visual inspection, and analyzing freeze frame data.
3) Throttle Issues
If you have a problem with the throttle body, your vehicle’s engine may be more likely to rev up on its own or stall at high speeds. This is especially true if your engine’s throttle plate is stuck in its own hole, as can happen if the throttle plate is contaminated with carbon.
How to fix the problem: Regularly cleaning your engine’s throttle body will prevent excess carbon buildup and prevent this type of problem. If you suspect your vehicle already has this type of problem, a thorough visual inspection is recommended.
4) IAC valve failure
When idling, the vehicle’s throttle body is completely blocked and the internal throttle valve remains in the closed position. A very small amount of air passes through the passages, and enough air is sucked in to maintain the idle. This airflow is measured by the idle air control valve (IAC). A faulty IAC valve often results in an abnormally high idle in parking mode.
How to fix the problem: The idle air control valve must be properly tested to ensure the integrity of the electrical circuit. Apart from this, carbon buildup on the IAC spigot is also commonly observed and should be cleaned regularly.
5) Sticking EGR valve
The EGR valve on your engine allows a limited amount of exhaust gases into the intake for further combustion. Ideally, this valve should only be able to open when the engine is warm and under load. However, the EGR valve can stick, causing a high or erratic idle.
How to fix the problem: Often, simply cleaning the carbon deposits on the affected EGR valve will get it working again. In other cases, replacement may eventually be necessary. This often occurs when the EGR valve begins to fail electrically.
6) Fouled Spark Plugs
To achieve the highest possible operating efficiency, each engine’s spark plugs must have a precise electrode gap and be free of contaminants. If one or more spark plugs become fouled or damaged, engine performance will quickly decrease, often resulting in rough idling and increased engine speed.
How to fix the problem: Your vehicle’s spark plugs should be replaced according to the recommended maintenance schedule provided by your vehicle manufacturer. Apart from that, it is highly recommended that you have all your spark plugs inspected on a regular basis.
7) Inoperative Fuel Injector
A fuel injector must be maintained in optimal condition, in order to atomize fuel as designed. If a fuel injector were to fail or become clogged, a number of secondary symptoms can be observed. One of the most notable of these symptoms involves a noticeable hunting or surfing in RPM, especially at idle.
How To Fix: One should promptly test their vehicle’s fuel injectors for function, should they prove suspect. This can be easily done with the use of a bidirectional scan tool. Additionally, clogged fuel injectors can often be salvaged through careful cleaning.
Identifying the Source
In virtually every case, unanticipated engine revving comes down to the fault of one of three conditions:
Irregular spark distribution
Most mechanics lean heavily upon this knowledge when diagnosing issues of this type, seeking to check the health of each of these three critical systems as a whole.
Potential Downsides of a Car Revving On Its Own
There are several downsides of note when it comes to a vehicle that seems to rev spontaneously. Additionally, a vehicle that revs in an unexpected fashion is largely a safety hazard, to say the least.
