Rough idle and RPM fluctuation

truck has a very rough idle, today I replace both vct soilnoids and it did not help have a check engine is on runs better with overtime off, two years ago I have both timming chains replaced and plugs too. runs fine on the highway.

My car has 160000 miles.
My car has an automatic transmission.

Experienced mechanics share their insights in answering this question :
This may be related to a dirty or failing idle air control valve. The idle air control valve reads 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 which will adjust idle speed based upon other measurements such as engine temperature, intake air temperature and electrical system load or voltage. When you accelerate, the engine RPM increases, and as you let off the gas, the RPM slowly returns to the normal idling speed. This is all controlled by the idle air control valve. When the engine RPM drops below the normal range of 750-800 RPM (for most cars), 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 repair your idle air control valve.

How to Identify and Fix Common car Problems ?

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The most common reasons a Ford F-150 has rough idle are a vacuum leak, an issue with the spark plugs, or a problem with the ignition coil.
Here are a few reasons a Ford F150 might shake at idle:

Spark plug issue. Vacuum leak. Ignition cell fault.

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.
Common reasons for this to happen:

A defective TCS or torque converter solenoid can also cause this issue. Low fuel pressure, dirty or defective fuel injectors, or broken fuel pump: The fuel pump is responsible for transferring fuel from the tank to the engine.

Engine Misfires

Perhaps the single most common cause of rough idle comes in the form of a misfiring engine. As you may know, any automotive engine contains multiple cylinders. Each of these cylinders contributes to powering your car by combusting a mixture of gasoline and air.

Causes of a rough idle. Many different problems could result in a rough idle for your car or truck, including: dirty fuel injectors, clogged air filters, bad spark plugs, and a variety of exhaust system issues.
One of the main reasons why your vehicle could be vibrating at idle could be due to worn out spark plugs. When a vehicle`s spark plug is faulty, it can interfere with the air-fuel ratio leading to improperly firing cylinders, resulting in a misfire while idling. Replacing your spark plugs will solve this problem.
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.
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 an engine is not getting enough fuel (this is called “running lean”), due to fuel pressure (regulated by the fuel pump and regulator), restricted fuel injectors, a vacuum leak or really anything that throws off the fuel mixture going in to the engine, this can cause the surge.
Generally, the cause of a misfire at idle is an incorrect air-fuel mixture. This can be caused by a faulty O2 sensor, a fuel injector that needs cleaning, or even vacuum leaks.
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.

Your engine fuel injectors can collect grime, dirt, and soot leading to an air-fuel mixture imbalance for your car. When this happens, you may notice poor performance, rough idling, and inconsistent gas mileage over time.
Ford F 150 jerk on acceleration can be caused by an oil pan gasket, which may need to be replaced. Ford F 150 jerk on acceleration can also be caused by a faulty throttle positioning sensor. If the vehicle jerks when accelerating, this will cause an increase in fuel consumption and may need to be replaced.
The Ford death wobble defect may be caused by premature wear or loosening of various components such as the ball joints, control arms, track bar bashing, damper bracket, or shocks. Unfortunately, fixing the problem involves trial and error.
One of the most common causes of a sputtering engine is an issue with the vehicle`s fuel system—the filter, pump, and injectors. These three critical components work together to ensure fuel flows smoothly from the fuel tank to your engine`s fuel injectors, and then pumps into the engine evenly.
Engine Issues

Often, this shaking or shuddering will be emitted from the engine department. The most common reasons for this include: A dirty or clogged fuel filter. Spark plugs that are not running smoothly. Poor air/fuel mixture in the piston.

Causes of RPM Fluctuation While Driving

Many RPM fluctuations are caused by transmission problems. It can also happen when the spark plugs are dirty or if there is a vacuum leak that causes misfires. In some cases, the crankshaft position sensor may send the wrong engine speed signal to the tachometer.

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.
With respect to our problem of rough running, an EGR valve can be a cause if it becomes fouled with carbon. This causes it to stick open, causing a rough idle or engine stall. As explained earlier, in many cases, the computer may set codes that can lead you to the EGR valve as the problem.
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.
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.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

Idles between 500rpm and 1300 rpm. Main concern is low rpm. Belt or pulley chirping mainly at low rpm Drives perfect but Idles bad
ANSWER : Hello. From what you describe it would appear that your vehicle may have more than one issue.

Belt chirping is usually caused by a worn belt or tensioner. If either component wears out the belt may loosen and chirp when the engine is started, or cold.

The low rpm low quality idle can be caused by a few different things. I would look at the idle air control valve, as that is the component that maintains the vehicle idle, and at any vacuum hoses that may be cracked or damaged, and possibly leaking. This is more likely for older or high mileage vehicles.

If you’re unable to pinpoint the issue yourself, consider YourMechanic, as one of our mobile technicians will be able to come to your home or office to diagnose your starting issue firsthand and make the necessary repair to your car.

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The car idles rough and is shooting out codes p0017, p0016.
ANSWER : Hello. This is a common problem with the variable valve timing solenoid on this engine. I have changed quite a few of these due to failure. I always start by checking the codes and testing the solenoids and the connectors as some of the time the connectors fail and have poor connections. There have been a few times that I have seen these codes due to low oil or the wrong oil and from the camshaft actuators failing, but most of the time it is due to the solenoids. If you are planning on having this fixed, consider YourMechanic, as a certified mechanic can come to your home or office to diagnose and repair the rough idling issue for you.

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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.

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My 2003 Mazda Tribute stalls in gear, no power, rough idle, not the plugs, oil fouled black, clean maf and idle air valve
ANSWER : Hello. I would start by scanning the vehicle for codes and checking to see if all of the sensors are reading correctly. If everything looks good then chances are it needs a new computer. I have seen the computers fail on these vehicles over and over again causing the ignition circuits to not work correctly which causes the vehicle to run just like this. If you need to have this looked at, consider YourMechanic, as a certified mechanic can come to you to [diagnose why the vehicle is running like this] https://www.yourmechanic.com/services/car-idle-is-rough-inspection

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12 so ic 1.8 5 speed motor blow up replaced it idle is rough spits and sputter has no power to go up a hill no check engine light
ANSWER : The issue you are writing in about is common enough that a specific diagnostic, namely a reduced engine power diagnostic is performed by technicians dispatched by YourMechanic. If you request that diagnostic, the responding certified mechanic will get this issue resolved for you. In your circumstance, the vehicle’s powertrain control module (PCM) has undoubtedly stored one or more diagnostic trouble codes that will identify the "general area" in which the fault lies in the engine management controls. Although the throttle control system is a common trouble area with reduced power, there are quite a few other components and systems that could come into play and, of course, there is always the possibility of multiple, or "coincident", faults. Here are some of the possibilities that YourMechanic dispatched technicians would consider:

Defective throttle position (TP) sensor
Defective oxygen sensor
Defective accelerator pedal position (APP) sensor
Loose or damaged wiring
Defective throttle body
Defective powertrain control module (PCM) (not typical; ONLY if a long, long list of other possibilities is ruled out)
Any fault/error that will affect drivability function
Any fault/error that will affect vehicle performance
A fault/error in the emissions system
A fault/error in the throttle control system
A fault/error in the transmission control system

If you request the recommended diagnostic the mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

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Rough idle, fluctuating rpms, stalling
ANSWER : Hello, thank you for writing in. The vehicle is struggling to keep up with all of the different accessories when the engine is idling. This is typically due to an issue with the air intake, fuel intake, or the sensors that monitor and control them. Start by having the vehicle scanned for codes at your local automotive parts store, or by a different technician. If no codes are present, attempt to clean the throttle body, idle air control valve, and the throttle position sensor. If there are codes present, then you can use them to point you to the issue at hand, and take corrective action from there. For more help with diagnostics or resolving the issue, contact our service department to schedule an appointment.

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High idling, jumping while idling, idle air control valve code
ANSWER : Hi there. This can be caused by the issues that you mentioned or a number of other things. You need to make sure all of the connectors are making good contact. I would then need to know what codes are in the computer to know if this is a circuit issue or not. Most of the time, it is not the circuit but instead a vacuum leak.

If there is a vacuum leak, then the vehicle will act like this and the computer cannot control the idle. Most of the time it is a bad hose or an EGR valve that is stuck open. That is the most common cause for this. I typically remove the EGR to check it to feel the diaphragm on the bottom of it to see if it is moving correctly. If you need to have this repaired, consider YourMechanic, as a certified mechanic can come to your home or office to diagnose and repair your car’s idling issue.

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When my car is at idle in park or neutral the Intake Air Control Valve fluctuates, causing the RPM’s to do the same.
ANSWER : Hi there. It sounds as though the idle air control valve (IAC) may be sticking. It is not uncommon for carbon to build up in the valve, the computer will try to overcompensate to correct the slow reaction inside the IAC, and therefore the idle will fluctuate. It would be best to observe the commands from the PCM with a scan tool if you cannot physically see if there is carbon build up. A certified professional from YourMechanic can come to your car’s location to diagnose the idling problem and assist with repairs.

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