Car rev’s fluctuate when idling sometimes, happened twice in one week.
Twice this week (once while stopped in my garage and once at a red light) the rpm's on my car started to go up and down while I was idling. They would go so low that I thought my car would stall out.
The first time was in the garage. I turned my car off and then on again and it seemed to have 'fixed' the problem. When at the red light, once I started driving again, that seemed to 'fix' the problem.
What do you think may be causing this being that it's so infrequent.
The first time was in the garage. I turned my car off and then on again and it seemed to have 'fixed' the problem. When at the red light, once I started driving again, that seemed to 'fix' the problem.
What do you think may be causing this being that it's so infrequent.
My car has 209000 miles.
My car has an automatic transmission.
Experienced mechanics share their insights in answering this question :
Hi There,
What you are describing sounds like a dirty or faulty idle air control valve. The idle control valve reads the air intake into the throttle body and relays this information to the computer which then uses this information to make adjustments to the fueling of the motor. When this is not working properly, you may notice an erratic idle problem as you describe. I would suggest having a professional from YourMechanic come to your location to diagnose and inspect your vehicle.
What you are describing sounds like a dirty or faulty idle air control valve. The idle control valve reads the air intake into the throttle body and relays this information to the computer which then uses this information to make adjustments to the fueling of the motor. When this is not working properly, you may notice an erratic idle problem as you describe. I would suggest having a professional from YourMechanic come to your location to diagnose and inspect your vehicle.
How to Identify and Fix Common car Problems ?
Our sources include academic articles, blog posts, and personal essays from experienced mechanics :
Engine hunting and surging at idle is usually caused by a fuel delivery, air leak, or governor system problem. Cleaning/overhauling the carburettor, adjustment of the governor, and/or changing the air filer may be required.
The most common cause of the shaking most often happens near your tires and rims. The tires and wheels connect your vehicle to the road, and if anything is a bit wonky, will notice. It may be something like a broken transmission or a broken control arm.
The engine RPM drop when changing gears is often caused by a failed throttle position sensor (TPS). When in use, the cone of the TPS accumulates soot that prevents the correct rod movement. If a TPS works abnormally, the air-fuel mixture will not meet the requirements.
How to fix it? Cleaning or replacing the fuel filter and adding a fuel injector cleaning treatment to the fuel tank should take care of clogged fuel injectors. If the rough idle persists, it`s time to take your car to an auto repair shop.
Replace the sensor with a compatible one and correctly install the crankshaft position sensor to ensure that the engine runs optimally and safely. A qualified technician can prevent further issues with RPM fluctuations while driving by installing the sensor correctly.
If the alternator is dying and the battery isn`t fully charged you can expect all kinds of weird electrical problems to happen. The alternator output will fluctuate with changing RPM.
While it may seem like a small problem on its own, rough idling is a sign that some part of your engine isn`t working properly. Over time, rough idling can result in poor gas mileage, starting issues and major engine problems.
Oxygen (O2) sensor
An oxygen sensor monitors and analyzes the amount of oxygen in a vehicle`s exhaust system after combustion. A dirty, damaged or malfunctioning O2 sensor (or sensors) affects the air/fuel mixture, causing the engine to idle rough.
If your RPM starts fluctuating, there might be issues with the engine`s combustion process, a communication gap between the IAC and the ECU, or it can be a worn-out spark plug.
RPM fluctuation is a common symptom of worn-out spark plugs, especially in older vehicles. Spark plugs that are worn out are unable to correctly fire the fuel within the piston at the appropriate time.
Potential causes of a vehicle shaking at idle include a loose gas cap, loose battery cables, a worn throttle sensor, a damaged engine mount, or bad spark plugs. Perform a general inspection of your engine bay to look for damage. If you can`t repair the problem yourself, take the vehicle to a mechanic.
Low automatic transmission fluid can cause shaking. If the shaking is accompanied by the check engine light, it`s time to visit a mechanic. Drivers of manual cars might discover their clutch master cylinder is the source of the shaking.
If you begin to feel persistent shaking in your car, it`s best that you get to the problem right away before continuing to drive. Continuing to drive with the shaking can result in further damaging parts, ruining your tires, and other costly problems that could be avoided by a quick trip to your mechanic.
Improperly functioning spark plugs cause an uneven burn of fuel in the engine, resulting in fluctuating RPMs and a louder noise. You might also experience increased vibrations of your vehicle while sitting idle or while traveling at low speeds. These vibrations originate from the engine and can shake the entire car.
An idle air control valve, also called an idle air sensor control motor, is an electrically operated valve that controls the amount of air that bypasses the throttle plate in cars with a fuel injection system [source: Autozone]. This causes the idling speed of the engine to change as needed.
To check whether the idle air control valve is functioning properly, start the engine and let it run for about 10 to 15 minutes. If the valve is functioning correctly, the engine will sound good and the idle will be steady versus too high, too low, or inconsistent.
When the battery`s state of charge is low, the voltage is raised slightly to quickly put the charge back in. When the state of charge is high, the voltage is lowered slightly to prevent overcharging. If the vehicle has a voltmeter gauge, you may see the voltage move up or down. This is normal.
For regular cars, idle speed is typically between 600 and 1,000 rpm, just enough to keep the engine`s ancillary systems going, but not enough to move the car forward much.
Yes. While the damage may seem small initially, the longer you drive with a bad oxygen sensor, the worse the damage will become. Eventually, you may experience rough idling, poor acceleration, engine misfires, an illuminated check engine light, and failed emission tests.
Common culprits include the ignition control module, plug wires, coils, and spark plugs. Defective Airflow Sensor: A defective airflow sensor can be responsible for a rough idle. A mass airflow sensor detects the amount of air coming into the fuel injection system and sends that information to the vehicle`s computer.
While it may seem like a small problem on its own, rough idling is a sign that some part of your engine isn`t working properly. Over time, rough idling can result in poor gas mileage, starting issues and major engine problems.
Relevant Questions and Answers :
the most relevant questions and answers related to your specific issue
Car rev’s fluctuate when idling sometimes, happened twice in one week.
ANSWER : Hi There,
What you are describing sounds like a dirty or faulty idle air control valve. The idle control valve reads the air intake into the throttle body and relays this information to the computer which then uses this information to make adjustments to the fueling of the motor. When this is not working properly, you may notice an erratic idle problem as you describe. I would suggest having a professional from YourMechanic come to your location to diagnose and inspect your vehicle.
What you are describing sounds like a dirty or faulty idle air control valve. The idle control valve reads the air intake into the throttle body and relays this information to the computer which then uses this information to make adjustments to the fueling of the motor. When this is not working properly, you may notice an erratic idle problem as you describe. I would suggest having a professional from YourMechanic come to your location to diagnose and inspect your vehicle.
Read Full Q/A … : Car rev’s fluctuate when idling sometimes, happened twice in one week.
I put the wrong key in my car and a few weeks later my car just shut down and it will not start I believe it’s the computer but…
ANSWER : Hi there. What had happened is the wrong key set the security to the vehicle. This is to prevent the vehicle from starting with the wrong keys. Try removing the battery cables (+) and (-) for 13 minutes. During that time, put the original key in the ignition and turn it on. Activate everything in the car even though there is no power. Then remove the key and hook up the battery cables. The computer should have reset and reset the security. If the security is still being tripped, then I recommend seeking out a professional, such as one from Your Mechanic, to help you
Read Full Q/A … : Car rev’s fluctuate when idling sometimes, happened twice in one week.
My car revs by itself when idle sometimes the car jerks a little what is the problem?
ANSWER : It sounds like you may have a dirty or failing idle air control valve. The idle air control valve monitors the air intake as it is mixed with fuel prior to being injected into the engine at low speeds and at idle. This valve is controlled by the vehicle’s computer and will adjust idle speed based upon other measurements such as engine temperature, intake air temperature and electrical system load or voltage. This is also an important function when starting the motor as it allows the motor to run and idle on it’s own once the motor fires. When you accelerate, the engine RPM increases, and as you let off the gas, the RPM slowly returns to the normal idling speed with the help of the idle air control valve making the transition from a higher RPM back down to idle speed while adjusting the air/fuel ratio constantly to allow this to happen smoothly. When the engine RPM drops below the normal range of about ~800 RPM, this often times will cause the engine to stall indicating a dirty or faulty idle air control valve. I would recommend having an expert from YourMechanic come to your location to diagnose and inspect your vehicle.
Read Full Q/A … : Car rev’s fluctuate when idling sometimes, happened twice in one week.
When I’m driving, sometimes the car over revs and jerks when I shift gears after the cars been on for a while
ANSWER : Hi There,
What you are describing may be a result of a faulty speed sensor, potentially low transmission fluid or a even a faulty transmission control solenoid. As your vehicle travels down the road, the computer analyzes data being sent by vehicle speed sensors and engine speed sensors. Based on this information, the Engine Control Unit (ECU), or the Transmission Control Unit (TCM), executes the appropriate upshifts and downshifts by sending a signal to one of several shift solenoids. These transmission solenoids have spring-loaded plungers inside them, which are wrapped with wire. When this coil of wire receives an electrical charge from the TCM / ECU, it causes these plungers to open, allowing transmission fluid to flow into the valve body and pressurize the desired clutches and bands. When this happens, the transmission changes gears and you continue down the road. The computer controls the transmission solenoid in several ways. If the vehicle is equipped with a dedicated Transmission Control Unit, it can open or close the hydraulic circuit using a direct 12v signal. In some cases, the Engine Control Unit (ECU) can control the solenoid’s plunger by turning the ground circuit on and off. I would recommend having a professional from YourMechanic come to your location to diagnose and inspect your transmission.
What you are describing may be a result of a faulty speed sensor, potentially low transmission fluid or a even a faulty transmission control solenoid. As your vehicle travels down the road, the computer analyzes data being sent by vehicle speed sensors and engine speed sensors. Based on this information, the Engine Control Unit (ECU), or the Transmission Control Unit (TCM), executes the appropriate upshifts and downshifts by sending a signal to one of several shift solenoids. These transmission solenoids have spring-loaded plungers inside them, which are wrapped with wire. When this coil of wire receives an electrical charge from the TCM / ECU, it causes these plungers to open, allowing transmission fluid to flow into the valve body and pressurize the desired clutches and bands. When this happens, the transmission changes gears and you continue down the road. The computer controls the transmission solenoid in several ways. If the vehicle is equipped with a dedicated Transmission Control Unit, it can open or close the hydraulic circuit using a direct 12v signal. In some cases, the Engine Control Unit (ECU) can control the solenoid’s plunger by turning the ground circuit on and off. I would recommend having a professional from YourMechanic come to your location to diagnose and inspect your transmission.
Read Full Q/A … : Car rev’s fluctuate when idling sometimes, happened twice in one week.
When I drive it and come to a stop with my foot on the brake my car revs up and sometimes shuts off and I have to start up again 2006 Chevrolet Impala
ANSWER : Hi – first task is to read any problem codes, whether the Check Engine light is on or not. Most auto parts stores will do this for you for free on a "time-available" basis. Any codes extracted are useful for diagnostic purposes. Based on your symptoms, the throttle position sensor is a leading failure possibility. A malfunctioning idle air controller could also cause the unpredictable idling issues, but not a shut-off while driving. I recommend a car stalling inspection performed by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, and give you an accurate assessment of damage and cost estimate for repairs.
Read Full Q/A … : Car rev’s fluctuate when idling sometimes, happened twice in one week.
Hey when the car idles it revs up and down by like 300 revs or so and also when the car is off it doesn’t recognize its in park.
ANSWER : The issue is the transmission position sensor is not working properly and registering that the transmission is in drive, neutral, or reverse. Check to see if the transmission is going into park when the shifter is in park. If the transmission is going into park, then the sensor is not working and needs replaced. If the transmission is not going into park, then the shifter cable may be broken or out of adjustment. If you need further assistance with transmission not going into park issue, then seek out a professional, such as one from Your Mechanic, to help you.
Read Full Q/A … : Car rev’s fluctuate when idling sometimes, happened twice in one week.
Car is idling at high rpm’s and when the days are hot the car cranks but doesn’t turn on and also exhaust is smoking when i rev it
ANSWER : Hello – your symptoms suggest worn piston rings or valve stem seals (smoking), and a possible air leak in the intake, or idle air control valve sticking open (high idle). Both are signs of a higher-mileage engine with significant wear. I recommend an engine inspection performed by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, and give you an accurate assessment of damage and cost estimate for repairs.
Read Full Q/A … : Car rev’s fluctuate when idling sometimes, happened twice in one week.
After driving awhile, when idling, RPM drops below 500 & car stalls. Happens rarely but RPM fluctuates, and drops suddenly.
ANSWER : If you are having a stalling problem then you may have a computer code stored in memory. I suggest having the computer scanned to see if there is any codes stored and diagnose them as needed. The intake hose and air filter should be inspected for leaks in the hoses and dirty or leaking air filters. If the air filter is dirty or leaking then have the mass air sensor cleaned. If you still need help, have a mechanic diagnose the stalling issue for you and let you know exactly what repairs should be done.
Read Full Q/A … : Car rev’s fluctuate when idling sometimes, happened twice in one week.
