8 Reasons Your Car’s RPMs Fluctuate While Driving
When your car’s RPMs fluctuate, it’s a sign of trouble. As drivers, we know our car’s rhythm so well that the slightest hiccup sets off alarms. Fluctuations in engine speed while driving or accelerating often indicate a problem beneath the surface. Read on to find out what causes this problem, whether you should keep driving, and how much it might cost to repair.
Causes of Speed ​​Fluctuations While Driving
Understanding the possible causes of this condition will help diagnose the problem at hand. Below are some of the most common causes of speed fluctuations:
1) Vacuum Leaks
Vacuum leaks are one of the most common causes of speed fluctuations. This condition represents the ingress of unmetered air into the engine’s intake tract. This influx of air can disrupt the engine’s air-fuel ratio.
2) Ignition Issues
Insufficient spark output in the engine’s ignition system can also cause noticeable fluctuations in speed. These issues can include faulty spark plugs/wires, worn ignition coils, earthed external ignition coils, etc. In older vehicles, a damaged distributor cap can also affect the spark supply.
3) Fuel Supply Issues
Lack of fuel for combustion can cause engine speed irregularities. This type of problem can be caused by cylinder-specific issues related to clogged fuel filters, damaged fuel pumps, or even injector failure.
4) Throttle Position Sensor Failure
The throttle position sensor in your vehicle is responsible for providing feedback to the engine’s PCM regarding the throttle position. Any deviation in this feedback can result in wildly erratic or unstable engine operation and vehicle speed fluctuations.
5) Engine Speed ​​Sensor Failure
Almost all modern engines use one or more special speed sensors. These include the engine’s camshaft and/or crankshaft sensors, and the transmission speed sensor, which are the most common. When these sensors start to fail, a variety of strange symptoms can occur.
6) Faulty Idle Air Control Valve
If your engine speed fluctuates widely while idling, your vehicle’s idle air control valve (IAC) may be the culprit. This valve regulates the intake air flow when the engine throttle is closed. If the idle air control valve becomes burnt or damaged, it may function erratically at best. DTCs P0505, P0506, and P0507 are secondary symptoms of a defective IAC valve.
7) Transmission Issues
While not as common as the other possible causes on this list, internal transmission issues can actually affect engine operation. Slippage or lag within the transmission can often be detected when analyzing the engine’s speed.
8) PCM Failure
In rare cases, your vehicle’s PCM may fail on certain circuits, affecting how it responds to certain criteria and feedback. This can result in a variety of drivability-related issues, including affecting the engine’s operating speed.
