What is the no-load solenoid valve, principle of operation and troubleshooting

What functions the idling electromagnetic valve performs, how it works and its characteristic malfunctions

All automotive internal combustion engines are necessarily equipped with an idling system. This is relevant for injector, carburetor and diesel engines.

Idle speed solenoid valve

This system is required so that the engine behaves stably at idle speed (idling). In this state, the mounted throttle valve will be completely closed.

The system includes several components. But one of the key components is rightly considered the electromagnetic valve. He is also the idle speed regulator.

What is it for

To begin with here, it is necessary to understand what the CCS is and why it is used in the car.

The idle speed valve is responsible for the flow of the fuel-air mixture into the engine manifold. It uses a separate idling channel, which bypasses the main throttle flap itself. The latter is under the control of the throttle pedal.

Depending on what type of engine we are talking about, the valve can regulate the supply of the required volume of air or the fuel component. If it is a carburetor or diesel engine, then the fuel supply is regulated. If it’s a gasoline injector, then the right amount of air is delivered with the help of the CCX.

But it is not enough to know about the purpose of this idling system valve. It is also worth to understand the peculiarities of its operation.

Principle of operation

Next under consideration is the question of how the idling system valve, that is, the idling speed regulator, works on car engines.

The idling speed regulator itself is an electromechanical actuator, which is monitored and controlled by the engine ECU. The latter sends electrical signals, due to which the valve opens or closes. This changes the diameter of the no-load flow through which the required volume of air or fuel for the internal combustion engine enters the intake manifold.

To understand the principle of operation, on which the functioning of the idle speed regulator valve is based, it is worth considering the node on different types of engines.

Idle speed solenoid valve


In carburetors that run on gasoline, there is necessarily such a solenoid valve. It is located in the body of the carburetor itself and is part of the economizer of forced idling.

This valve is controlled through the economizer control unit, which is located in the underhood space. When the ignition is turned on, power is supplied from the block to the regulator and it opens and feeds fuel into the manifold through the idle channel. When the ignition is turned off, power to the valve is cut off and therefore the fuel supply is shut off.

To select the optimum fuel volume for the idle channel, a special adjustment screw is provided by the carburetor design.

This screw has received a quite logical name and is referred to as the idle speed screw.

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In gasoline injectors, the idling speed regulator operating principle is somewhat different. It is structurally located in the throttle body and is part of the electronic engine control system.

ECU is responsible for the valve operation. It records the signals coming from the control sensors installed, processes the data and transmits the control signals directly to the regulator itself. Due to the commands from the ECU, the RCD can increase or decrease the volume of air flowing into the engine manifold thus maintaining the set RPM.

Injector on a car engine


In the case of diesel, the solenoid valve is located in the housing of the HPF, that is, the high-pressure fuel pump. As in the case of the injector, there is a connection of the BCD with the internal combustion engine ECU.

A distinctive feature of the diesel engine is the regulation of fuel, but not air, to control the engine RPM.

In the rest, the principle of operation is similar to the gasoline injector.

Varieties of the throttle valve

Externally, the regulator somewhat resembles an electric motor with a conical needle in its design.

There are 3 types of such controllers.

  • Solenoid. The simplest regulators in terms of their device. When voltage is applied, the inner core on the winding is actuated and placed in a specially provided socket, which allows you to reduce the diameter of the passage channel. This reduces the air or fuel supply. The simple design reduces the cost of the product. This regulator can work only in fully open and closed position.
  • Step regulators. These VTCs consist of a winding and a special ring magnet. Totally there are four windings. Control signals from the ECU are applied to one of the windings, which contributes to the rotation of the rotor. Because of this the cross-section of the flow channel changes smoothly from full opening to full closing, and vice versa.
  • Rotary. Their principle of operation is similar to that of the solenoid VCF. But here, the task of the core is performed by the rotor. The latter is able to rotate in different directions, while changing the size of the channel cross-section.

Depending on the type of motor and its factory specifications, different types of regulators are used.

Idling speed valve

Diagnosis of the device

Motorists are interested in how to check independently the idling valve and its current state.

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For many motorists, an independent check of this valve, a component of the idling system, is quite a feasible task. There are several methods of diagnosing the condition of the regulator.

  1. External inspection. First, a visual inspection is carried out. This allows you to determine the presence of defects on the body, traces of needle wear, signs of fouling on the surfaces. If there are deposits, they can be removed with a carburetor cleaner. For sure, the whole throttle assembly will also be dirty with contamination of the throttle valve. Therefore, it won’t be superfluous to clean it as well.
  2. Diagnostic software. Some motorists switch to the use of special diagnostic software. In addition to the software, it is also required to have an adapter to connect to the system. Through the menu of the software, the position of the controller is selected and its operation is observed.
  3. The state of the wiring. It is not superfluous to thoroughly check the wiring, connected to the Binary Converter. A multimeter is required here. The engine is switched off, the sensor connector is removed. On the multimeter, select the voltage test mode with a limit of 0 to 20 V. If it is working properly, the instrument should show about 12 V.
  4. Resistance. The resistance of this regulator is also checked. To do this, use the same multimeter to check the resistance between the terminals by disconnecting the sensor terminals. The multimeter is switched to resistance mode, and the limits are set from 0 to 200 ohms. The leads are conventionally labeled A, B, C and D. When measuring resistance on A and C, as well as on B and C, the instrument should display infinity. In other cases 50-55 ohms is normal.
  5. Checking with a choke. Quite common among motorists and check with the throttle assembly. The complexity of the method is that you will have to dismantle the entire throttle assembly directly together with the sensor itself. Plugging in the RTC connector, turning the ignition on and off, visually observe the operation of the suspected regulator. Make sure the needle is running normally, the stroke is even, and there are no unusual noises.

Diagnostics of idling valve

In most cases, if the IAC fails, it is replaced with a similar part.

Signs of malfunction

The throttle valve is not the most vulnerable element of the engine, but its failure is quite possible.

The symptoms of ICA failure are largely similar to the symptoms of throttle position sensor failure.

But the throttle valve regulator belongs to the category of executive automobile devices, and therefore the Check lamp does not light up on the dashboard when it breaks down or malfunctions occur.

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You can find out about the regulator malfunction by the following symptoms:

  • The engine behaves unstably when the engine is idling. Sometimes the engine may spontaneously stall if the revolutions are not maintained with the gas.
  • Without any reason the rpm increases or decreases.
  • When shifting any gear, the engine may stop completely. A similar situation may occur when starting from a place.
  • When a cold start occurs, the engine does not run at higher revolutions.
  • Turning on the headlights or the cabin heater will cause the idle speed to drop.

Cleaning the regulator or replacing it completely can help in troubleshooting. It is not difficult to clean and then wash the part yourself, as well as to replace the element. But in both cases, it is better to first dismantle the controller.

To do this, turn off the engine and remove the minus terminal from the battery. Next, the connector of the controller contact is disconnected, the mounting bolts of the housing are unscrewed and the problematic element is removed.

Cleaning does not help in all situations. Before installing a rebuilt or new regulator, the flange o-ring should be lubricated with engine oil.

In the case of replacing the VFD, calibration is mandatory.

To calibrate the unit is simple enough with your own hands. To do this, it is necessary to:

  • Check the distance from the mounting plate to the end of the rod and make sure that it does not exceed 23 mm;
  • Disconnect minus from the battery;
  • install the new valve;
  • return the minus terminal back to its place;
  • switch on ignition for 5 seconds but don’t start the engine;
  • wait for automatic calibration;
  • switch off ignition;
  • fully start the engine and watch how it works at idle.

The idling speed regulator is an important component of any engine. At the same time its diagnostics, replacement and repair should not cause any special difficulties even for a novice.

Idling regulator (IAC) – how it works, malfunctions, symptoms, check

All modern cars have a regulator that maintains the idling speed. If idling speed loses stability, the cause may be in the sensor. To find out, you need to check the idling speed regulator (IAC).

idle speed regulator

Types and designs of idle speed regulators

The appearance of the sensor resembles an electric motor with a conical needle. The device is responsible for supplying the right amount of air bypassing the throttle valve at idling speed.

There are several varieties of such sensors:

  1. Solenoid-based. This is the simplest version of the device. When voltage is applied to the windings of the device, the core is actuated and placed in a special socket to reduce the diameter of the passage channel. As a result, there is less air supply. This regulator is cheap because of its simple design. This device works only in closed or open position.
  2. Stepper. It consists of windings and a ring magnet. Rotation of the main rotor is made by stepping voltage to all elements of the design under the influence of electromagnetic force. The opening of the air flow is regulated by the performing mechanism depending on where the rotor is located.
  3. Rotary. The air supply is regulated by alternating frequency pulses. The sensor design is similar to the solenoid PXX. The main role in the design is played by the rotor.
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How the regulator works

When the engine is idling, an additional air channel bypasses the closed throttle damper to provide the air needed for stable engine operation. The cross-section of this channel is regulated by the BCD. The amount of air is taken into account by the mass air flow sensor (DMRV). According to its quantity, the controller supplies fuel to the engine through the fuel injectors.

idling speed regulator idling speed regulator

The controller monitors the number of engine revolutions according to the crankshaft position sensor (CRS). Depending on the set mode, the throttle valve operates, adding or reducing air flow to bypass the closed throttle valve.

When the engine is warmed up to operating temperature, the controller maintains idling speed. If the engine is not warmed up, the controller increases the RPM at the expense of the regulator providing its warming up at higher RPM.

Signs of malfunction

The idling speed regulator is an actuating device and its self-diagnostics is not provided in the system. Therefore, the CHECK ENGINE lamp often does not illuminate in case of regulator malfunction. The symptoms of idle speed regulator malfunctions are largely similar to those of throttle position sensor (TPS), but in the second case the “CHECK ENGINE” lamp indicates the malfunction of TPS most often.

Symptoms of problems with the idle valve:

  • floating idling;
  • bad engine starting, especially in winter;
  • the car may stall on throttle dumping, after switching to neutral;
  • uncontrolled increase or decrease of idling RPM at normal engine temperature;
  • rpm drop after turning on headlights, air conditioner, heating system;
  • jerking of the vehicle while running at low RPM;
  • engine stalls when switching from low to high gear and vice versa.

These symptoms may appear all at once or separately.

Diagnose the sensor

You can check the idle speed valve yourself. Its faults can be divided into two parts: mechanical and electrical. There are several methods of checking.

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Visual inspection

To begin with, it is necessary to conduct a visual inspection. In this way, you can detect defects in the body, wear of the needle, the formation of fouling. In the case of the formation of deposits, you can clean with a carburetor cleaner. It is also recommended to clean the entire throttle assembly, since it is in a similar condition.

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Using diagnostic programs

You can check the operation of the v-torque converter with a diagnostic adapter and special programs. For example, you can use the simplest adapter ELM327 and the program OpenDiagMobile. In the menu of the program you need to select the desired position of the idling speed regulator and watch the work of the valve. It is better to set at least 20 steps more than the current position.

Checking of wiring

For this we need a multimeter. With the engine turned off, remove the connector from the sensor. Set the meter to the measurement range of 0-20V DC voltage. Measure the voltage at the connector. Normally it should be 12 V.

pxc voltage measurement

Checking the regulator resistance

To do this we need to measure the resistance between pins A, B, and C and D after disconnecting the sensor terminal. Set the multimeter to the position of resistance measurement at 0-200 ohms (Ω).

px resistance measurement diagram

The normal value is between 50-55 ohms. The resistance between A and C, B and D should be infinite.

Checking with Throttle Assembly

There is another way to diagnose the throttle valve. This will require removing the throttle assembly from the studs along with the sensor.

throttle assembly

With the valve connector plugged in and the ignition turned on/off, you can watch the operation of the idle valve live. See how the needle works, if it is mashing somewhere, check the uniformity of stroke, hear suspicious sounds.

Calibration of the new idle speed regulator

What to do, if after the test it turned out that the sensor is to be replaced? It is necessary to calibrate it.

piston rod distance

  1. Check the distance from the end of the rod to the mounting plate, it must not exceed 23 mm.
  2. Disconnect minus from the battery disconnecting ECU.
  3. Install regulator.
  4. Connect the battery back.
  5. Switch on ignition for 5 seconds without starting the engine. This is the time when calibration of the throttle valve takes place.
  6. Switch off ignition, completing calibration.
  7. Start the engine and observe idling.

Now you know how the idle speed regulator works, how to check it and replace it if necessary. As you have understood there is nothing complicated about it and all operations are available even to a novice car enthusiast.

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