Let me start today’s topic with a scenario. Suppose your hands are steady on the wheel for a long trip. For sure, everything is going just right. Suddenly, the engine is revving high like never before. You think,“ Why does my car rev high before it shifts?” If this scenario feels familiar to you, I welcome you to be a part of this discussion.
Typically, when you accelerate, your car shifts gears to match the right balance of power and speed. If the vehicle revs like a racecar champ before you shift gear, it may happen due to several factors. Well, these factors include clogged fuel filters and exhaust systems, faulty sensors, fuel pressure regulators, idle air control valves, and others.
Besides these factors, there is more to give a boost to your car before it shifts. In this blog, I will explain each of them to give you complete ideas on this topic. Additionally, you will learn the ways to deal with them. I hope you will not mind spending a few minutes reading this!
Cause of Car Revving High Before It Shifts
Cars have a common feature – an automatic transmission system. It allows the driver to shift between gears smoothly and conveniently. But it can be concerning if a car’s engine revs at high RPMs before shifting gears. In this part, I will discuss the reasons for and solutions to this problem.
Reason: 1 – Clogged Fuel/Transmission Filter
FYI, your car’s fuel filter keeps the engine fuel clean by removing dirt, debris, and other contaminants. But when it becomes clogged, it cannot effectively filter the fuel. So, the buildup of pollutants can cause the engine to rev high before shifting.
Some symptoms of a clogged fuel filter are hesitation of the engine, abnormal fuel flow, and reduced engine power (1). Again, the check engine light may turn on for the low fuel pressure caused by a bad filter (2).
Other signs include poor engine performance, like hard starting, hesitation, sputtering, or surging, especially under heavy load (3). Even a partially blocked filter can cause engine misfire, poor fuel mileage, rough idling, and possibly engine backfire or increased engine smog (4).
What to Do
You should keep your car’s fuel filter clean to get the correct flow of fuel to the engine. It will prevent the car from unnecessarily high revs before it shifts. To clean the fuel filter, follow these steps:
- Locate the fuel filter and disconnect the negative terminal on your car’s battery.
- Now, prep a container under the filter.
- Spray the filter with a pressurized carbon cleaner.
- Tap out loosened debris and let the filter dry for an hour.
- Reinstall the filter.
If your filter is nylon or paper, you should replace it with a new one instead of cleaning it (5)
Reason: 2 – Clogged Exhaust System
An exhaust system removes gases from the engine. But when it is clogged, it cannot push out the gas outside. As a result, it causes the engine to rev high before shifting.
You can identify a clogged exhaust system by some indicators. For example, the engine will produce low power and take more time to accelerate than usual. Well, it indicates that emissions are trapped in front of the catalytic converter (6). Other signs can be engine misfire, a sudden decrease in acceleration power and fuel efficiency. Moreover, it can disrupt the vehicle’s air-fuel ratio which may impact engine performance.
What to Do
You should clean the exhaust to keep the car’s transmission system smooth. You can follow these methods to clean an exhaust system:
- First, take a specifically formulated cleaning solution and pour it into the fuel tank to unclog the catalytic converter (6). In this case, you can apply a degreaser to break up carbon deposits and rust. Take a dry cloth to apply the degreaser to both sides of the exhaust system (7).
- Then, clean the exhaust manifolds as they may get covered with carbon buildup, soot, grease, etc., over time. Remove them to clean properly.
- Warm up the car if your exhaust pipe gets clogged with ice. Yet I don’t suggest you to use a salt solution or warm water to melt the ice (8).
Reason: 3 – Faulty Sensors
Do you know that any car you drive has multiple sensors like Mass Air Flow (MAF), oxygen, and speed? When these sensors have any issue, they can be a headache to drive the car smoothly. Also, they can cause your car to rev at high RPM before shifting gears.
For instance, a faulty MAF can cause rough acceleration, idling, and changes in fuel consumption (9). Also, the vehicle may hesitate or jerk forward while accelerating. Other symptoms include hard starting, the check engine light on, and engine hiccups.
Then again, a faulty oxygen sensor can indeed affect the shifting of a car. It can cause transmission problems, including difficulty shifting gears, poor performance, slipping, and jerking of the vehicle (10). It happens as the malfunction provokes the sensor to send false readings to car’s computer. In return, the engine addresses incorrect fuel intake and emission systems, and you get rough driving (11).
For sure, the speed sensor is a crucial part of the automatic transmission of any car. It senses when to change gear. Usually, these sensors can read how fast the output shaft spins (12). But when this sensor becomes defective, you will get high RPM before shifting the gear.
However, some signs of bad speed sensors are the check engine light on and startup problems. Also, the transmission may engage into overdrive late or not at all (13). Even the car’s brakes may sometimes be more complex than usual when coasting.
What to Do
All you need to do is troubleshoot the particular sensor after inspection. You can use an OBD II scanner to check for error codes related to these sensors. Then, I suggest you follow these instructions:
MAF Sensor Troubleshooting
- Clean the dirty sensor using a specialized cleaner and a soft-bristled brush (15). It is good if you follow the manufacturer’s instructions and avoid touching the sensor wires.
- Now, replace the MAF sensor if it fails to work after cleaning it. Purchase a new one to replace the old one.
- In some cases, you can bypass the MAF sensor to temporarily solve the problem (16).
Faulty Oxygen Sensor Troubleshooting
- Typically, cars have between 2 to 4 oxygen sensors. So, like MAF sensor, you can check for error codes relevant to the oxygen sensor (17). Also, look for any physical damage or corrosion.
- You can replace the faulty sensor with a new one. These sensors are available in most nearby auto parts shops or online marketplaces.
Bad Speed Sensor Troubleshooting
- Locate the speed sensor connection point. It will be on the WorkStation circuit board or WAGO module within the PowerNet controller.
- Now, remove the speed sensor connector plug and measure the resistance across pins “A” to “B”. The measured resistance should be around 1K ohms on p/n: 11026. If you read an open loop, check the speed sensor, connector, and wiring for breaks (18).
- You can remove the speed sensor connector plug or wiring. Then, check for 12VDC or 24VDC as the standard value (sensor dependent) at the connection point of power and ground wires.
- If you cannot get any readings of voltage, then the controller is not powering the sensor.
- Replace the faulty speed sensor with a compatible and matching item.
Reason: 4 – Faulty Fuel Pressure Regulator
I guess you have heard about it, right? It controls the amount of fuel delivered to the engine. But when a fuel pressure becomes faulty, it can provide too much or too little fuel to the engine. As a result, your car gets high rev before shifting.
Some signs of a faulty regulator are engine misfire and the check engine light on (19). Other signs may include black smoke from the exhaust, poor fuel economy, and fuel leaks (20). Again, the vehicle may experience rough idling, engine backfires, and poor acceleration (21).
What to Do
You need to clean or replace the fuel pressure regulator to prevent the engine from revving high before shifting gears. Follow these steps to troubleshoot a faulty component:
- Take a fuel pressure gauge to test the pressure at the fuel rail or fuel line (22). Too high or too low pressure may indicate a problem with the regulator.
- For too high fuel pressure, check the vacuum hose connected to the fuel pressure regulator for any cracks or leaks (23).
- Clean the regulator using a specialized cleaner and a soft-bristled brush (23). But you may replace the device if cleaning does not solve the problem. I want you to be sure to choose the correct regulator for your vehicle make and model.
Reason: 5 – Faulty Idle Air Control Valve
Let’s focus on idle air control valves. Well, they control the amount of air entering the engine at idle. However, a defective valve can allow too much or too little air into the engine. So, you may get high RPM revs before shifting.
Some common symptoms of bad idle air control valves are engine stalling, rough idle, and engine backfires (24).
If the valve sticks in the closed position, the idle speed may be too low. Hence, it will cause the car to feel like it’s about to stall. Alternatively, the idle speed may be too high when the valve sticks in the open position. Your car engine will run fast even when you do not drive the car (25).
What to Do
To solve the valve problem, start by cleaning it to remove dirt and other clogging materials. In this case, valve cleaners for automobiles will work better. Next, reset the valve by depressing the accelerator pedal slightly. Then, turn the ignition ON, start the engine, and let it run for 5 seconds or so (26).
Replace the idle air control valve if resetting and cleaning do not work well. Like other parts, you can buy it too from the auto parts stores.
Conclusion
Aha! I guess you have enjoyed reading this blog on “Why does my car rev high before it shifts?” Have you understood it? Well, I am summarizing the whole thing again.
Your car may rev high before changing gears – that’s what you are concerned about.
It may happen due to a clogged fuel filter and exhaust system, faulty sensors and fuel pressure regulator, and defective idle air control valve. Additionally, flawed fuel pump, dirty spark plugs, and catalytic converter can also be the reasons.
I hope you have understood my explanation, right? Still, if you have any questions, leave me a reply. It will take only a few moments!
Thanks for reading this blog.
