Idle air control valve перевод

Measuring an idle air control valve

Actuator information

Type: Air bypass control valve
Power supply: 12 V from system relay
Signal type: Varying in duty cycle
Signal level: 0 V to 12 V

Workings of an idle air control valve

To control the idle speed of an engine, an idle air control valve mechanism can be used. It controls the amount of air that bypasses the throttle valve. This mechanism is commonly used on vehicles with fuel-injection which have no throttle valve controller motor, like e.g. a throttle valve control DC motor or throttle valve position stepper motor.

Two different idle air control valves are found, with a single solenoid or with double solenoids, respectively having a 2-pin connection or a 3-pin connection. Both air control valves are mechanically similar in construction. The double solenoid valve uses one solenoid for opening and one solenoid for closing the valve. The single solenoid valve has a spring to pull back the valve in an initial position, usually closed, and the solenoid opens the valve against the spring pressure. Both idle air control valves have a power supply connected to one side of the solenoid(s) and the other side connected to the ECU. When the ECU needs to change the position of the valve it activates the solenoid by switching the solenoid to ground with a duty cycle signal, creating a magnetic field that pulls the valve to the new position. The duty cycle value affects the position of the valve and therefor the amount of air bypassing the throttle valve.

In this measurement, the used idle air control valve has 2 solenoids. The duty cycle frequency of an idle air control valve solenoid is about 100 Hz, other motor management systems can have different frequencies. The duty cycle signal at idle is usually 40-45% for the opening solenoid and the opposite for the closing solenoid, so 60-55%. In case of a single solenoid idle air control valve only the opening duty cycle applies.

Connecting the lab scope

Correct functioning of the idle air control valve can be checked by measuring the following signal voltages, see figure 1:

Channel Probe Voltage Range
1 Signal voltage opening solenoid 20 V
Ground at battery
2 Signal voltage closing solenoid 20 V
Ground at battery
3 Power supply at idle air control valve 20 V
Ground at battery

The lab scope is connected to the idle air control valve via a Measure lead TP-C1812B and Back Probe TP-BP85 and is set to recorder mode.

In recorder mode a streaming measurement is performed, continuously displaying the signals live on screen. Because the measured signals vary slowly, the Automotive Test Scope ATS5004D is set to a slow measuring speed.


Figure 3 shows a waveform of an idle air control valve of a car under the following conditions: key on, starting engine, idling engine, key off. This signal can be downloaded and used to correctly set up the lab scope or as reference signal.

Figure 3: Lab scope measurement of a idle air control valve

Channel 1 (red) shows the opening solenoid signal voltage, channel 2 (yellow) the closing solenoid signal voltage and channel 3 (green) shows the power supply voltage. The purple signal shows a calculated duty cycle signal from the opening solenoid, channel 1, and the meter shows the current duty cycle of channel 1. At the beginning of the measurement the key is turned on and the power supply voltage of the idle air control valve reaches 12 V. The duty cycle reaches 100% which means the bypass valve is opened completely, the ECU uses this to reset the position of the idle control valve. Subsequently the ECU sets the duty cycle signal to a setting that matches the current engine state. When the engine is started, the power supply voltage drops because of the engine starting. The ECU increases the duty cycle to allow the intake of air for the cold start. With no acceleration, the ECU adjusts the duty cycle to stabilize the engine speed to the correct idle speed. When the key is switched off, the power supply and the control signals are switched off.


Signal values may differ on different types of engine control units and idle air control valves. Consult ATIS for information on specific engine control units and idle air control valves.

The following signal deviations can indicate a problem:

  • No signal:
    Cause: back probes have no connection (perform a connection test), no power supply to idle air control valve, idle air control valve defective, ECU defective
  • Signal voltage too low:
    Cause: back probes have a poor connection (perform a connection test), poor power supply to idle air control valve, poor or no ground for the ECU, resistance in wiring to ECU
  • Noisy signal:
    Cause: wires of power supply or signal damaged, poor connection in connector terminals, defective idle air control valve
  • Signal shows an offset in relation to the example signal:
    Cause: scope is not set to DC coupling: , poor power supply to idle air control valve, poor or no ground for the ECU, resistance in wiring to ECU

Idle Air Control Valve



First of all, first post. 1991 2-door DX 4 Speed 3e-e 279,000 miles original engine.

How can you tell if the IAC valve is defective? My car has a horrible time at warm idle. I have gone through the thermostat, coolant temp sensor, and replaced the radiator cap. Can’t find a vacuum leak anywhere, but when I stick my finger into the IAC vale opening prior to the throttle body, the car idles right where it should. It also takes forever to warm up, and the temperature gauge rarely, if ever, gets to the half-way point.

I’m just about to rip apart the throttle body and IAC, but first of all I want some kind of direction on how this valve works before I do this. Also how do you get the air out of cooling system on this car? Most cars have a bleed valve somewhere, but not on this car. Thanks for any help!

Tercel GTS

N/A bites



Straight from the factory manual-

At low temp Coolant temp below 176F: When the air port is closed th RPM should drop.

After warm up: When the air port is closed, engine rpm should not drop more then 50RPM

If operation is not as specified, replace.

I have opposable thumbs I WILL prevail.

’92 Paseo – 4E-FTE, Poly engine mounts/full front bushings, Whiteline rear swaybar, 3in exhaust.:whatwhat:

Coming soon – Built 5E, ACIS int mani, Starion FMIC. :thumbsup:

Tercel GTS

N/A bites



It has a spring loaded valve in there. I don’t know if a repair kit can be had for it but it may be at a dealership.

I have opposable thumbs I WILL prevail.

’92 Paseo – 4E-FTE, Poly engine mounts/full front bushings, Whiteline rear swaybar, 3in exhaust.:whatwhat:

Coming soon – Built 5E, ACIS int mani, Starion FMIC. :thumbsup:



It has a spring loaded valve in there. I don’t know if a repair kit can be had for it but it may be at a dealership.

Thanks for the help. This is the only car that I own that I don’t have the factory manual on. But it’s so darned reliable that I haven’t needed it yet.

And I’ll try filling the coolant by removing the top hose. It makes sense, but my american and british cars can never be that simple.

I’ll rip everything apart tonight and see what shakes out.

Tercel GTS

N/A bites



I found out about the filling trick by accident when swapping an engine in a camry once.

Oh that’s always the best way. :headbang:

Took apart the throttle body removed the IAC and inspected it. It’ just a thermostat with a calibrated air opening. Threw it in boiling water and it shut, so it appears that I had a air bubble that prevented the flow of coolant through the passage keeping it open all the time. I’ll make sure there are no blockages leading up to the IAC. Then put everything back together and use your filling procedure.

I might see if I can get a T fitting somewhere so I can bleed the air out before the IAC.

Thanks again for the help!



Every thing is back together, and it does the same stuff. Except it heats up much faster. In hooking everything back up I unhooked the MAP sensor vacuum line and it idled like a champ. Is the sensor bad or do I have a vacuum leak somewhere? I don’t have a vacuum pump to test it. Thanks again!



Problem was a blocked coolant return hose from the IAC. The blockage was in the metal return line that meets the hose from the heater core. Used spray straw from my FI cleaner can and now it flows normally. Hopefully the gas mileage gets much better from here on out. I’ll change the plugs from running so rich.

I found the following and it helped me out.

From Motor, January 2000 by Dan Marinucci

Surging Idle
You may encounter a Toyota engine that surges rhythmically up and down between idle speed and about 1800 rpm. The root cause of this problem, which occurs on engines equipped with a coolant-heated fast-idle valve, very often is a low coolant level due to a leak or careless cooling,system service.

Experience shows that this problem is most likely to occur on 1987-91 Corollas, MR2s and FX16s N,,dth the 4AGE engine; 1988-93 Corollas and Celicas with the 4A-FE engine; 1988-94 trucks and 4Runners with the 3N7-1,-E engine; and 1990-94 Tercels mid Paseos xs,th the:3E-E and 5E-FE powerplants.

First of all, the fast-idle valves on these engines, which are mounted on the throttle housing, work in the traditional way. When the engine is cold, the valve opens, bypassing enough air around the throttle blade to establish fast idle. As the engine warms up, coolant heats the valve, gradually closing off this controlled air leA and bringing the engine down to curb idle speed. When these valves fail, they usually stick fully closed (no fast idle) or fully open (high, surging idle speed).

Note that when the fast-idle valve fails to close on a warmed-up engine, the PCM senses a combination of relatively high rpm and a closed-throttle signal at the same time. If the computer detects these two conditions at Operating temperature, it concludes that the engine is decelerating, and begins shutting off injectors-commonly called fuel cut-to reduce decel hydrocarbons (HCs). The fuel cut command causes the engine to surge up and down rhythmically.

The easiest way to diagnose this problem is to temporarily remove the closed-throttle signal by opening the IDL contacts inside the TPS/throttle switch assembly. You can do this by opening the throttle slightly or by pulling the harness connector off the TPS/throttle switch. If this stops the surging idle speed, check for low coolant and cooling system leaks first. Maybe someone else serviced the cooling system carelessly and all the system needs is a careful bleeding.

If the fast idle valve still seems to be hanging open, check coolant circulation. Both the inlet and outlet hoses on the valve should feel about the same– hot. When the fast-idle valve is bolted to the throttle housing on a Toyota equipped with a MAP sensor, testing for a stuck-open valve is easy: just remove the intake tube, start the engine and locate the air inlet hole for the fast– idle valve inside the throttle housing. If you feel suction at this inlet hole after the engine warms up, it proves that the fast-idle valve is stuck open.

When the fast-idle valve is mounted on the throttle housing of an engine equipped with an airflow sensor, you can’t use the test just described because the engine won’t run with the air duct disconnected. Instead, wipe off the inlet hole inside the throttle housing with a solvent that dries quickly and leaves no residue. Then cover the inlet hole with a piece of duct tape, reinstall the intake air tube and start the engine. If the engine idles normally with the duct tape in place, that’s proof positive that the fast-idle valve is stuck open.

5 Symptoms of a Bad Idle Air Control Valve (and Replacement Cost)

When the engine is running but the vehicle is not moving, this means the engine is idling. During this time, the number of revolutions per minute (RPM) inside the engine will change.

The idle air control valve is responsible for managing the engine idle speed. The valve is a major management component of the engine which will either decrease or increase the number of revolutions per minute, depending on what the current operating conditions call for.

The valve is connected to the throttle body next to the intake manifold. The engine control unit is what manages the function of the valve. Based on the information it receives like engine load and temperature, it will change the speed of the idle accordingly.

Table of Contents

How an Idle Air Control Valve Works

Engine speed refers to the number of revolutions it makes per minute. This is commonly referred to as the RPM. The current operating conditions of your vehicle will cause the idle air control valve to either increase or decrease the RPM in your engine.

For instance, if your vehicle has a heavy load or it is heating up too quickly, then the idle air control valve will adjust the RPM by increasing or decreasing it; respectively. This will allow the engine to handle the heavier load or cool down in each case.

The engine control unit is responsible for managing the idle air control valve. When this central computer receives information about the temperature and load of the engine, it uses this information to make the proper adjustments to the idle air control valve.

That way, the valve will regulate the engine RPM properly based on the information relayed from the computer.

Bad Idle Air Control Valve Symptoms

When you have a bad idle air control valve in your car, there are several problems and symptoms that will present themselves. If you don’t get the valve replaced immediately, your car will become undriveable.

Below are the top 5 symptoms of a bad idle air control valve which you will easily notice.

1) Intermittent Idle Speed

Since the idle air control valve is supposed to manage the idle speed of the engine, a bad valve will certainly throw that out of whack. It will cause the idle speed to randomly fluctuate to different speeds rather than stay at one constant speed.

The idle speed may be too high at one moment and then too low at other moments. You will clearly notice this idle speed changing by simply looking at the tachometer on the dashboard.

2) Check Engine Warning Light

Whenever there is the smallest problem or issue with anything connected to the engine, it will cause the central computer to activate the check engine warning light on the dashboard. A bad idle air control valve could certainly be one reason for this to happen.

If the number of revolutions per minute seems peculiar to the engine control unit, it will let you know by activating the warning light.

Of course, there could be a whole list of other reasons for the warning light to come on too. In any case, you should take your vehicle to the auto shop to get it checked out at once.

3) Rough Idling

A normal healthy idle air control valve will provide smooth idling in your vehicle. But if the valve goes bad for any reason, the idling will go from smooth to rough.

A rough idle will result in intense vibrations forming whenever your vehicle is stopped with the engine running. Since less air will be going into the engine during its idle state, the car will react by shaking profusely.

4) Engine Stalling

If you experience engine stalling from a bad idle air control valve, then you won’t be able to drive your vehicle at all. As soon as you start your car, the idle air control valve will immediately malfunction.

If you happen to be away from home and this happens, the stalling will happen every couple of minutes in the beginning. You should be able to make it to the nearest mechanic in time before the engine stalls completely.

5) Load Causes Stalling

Sometimes the engine stalling will happen on its own while other times, increasing the load on the engine will cause it to stall.

For example, if you turn on your heater or air conditioner when you have a bad idle air control valve, then your engine will probably stall immediately afterward. The steering wheel might also feel like it’s being dragged to one side too.

To temporarily fix this problem, just turn off your heater or air conditioner to reduce the load. Then let the engine cool for a couple of minutes.

Idle Air Control Valve Replacement Cost

If a voltmeter shows a reading outside of the normal range, then you need to purchase a new idle air control valve. Unless you know a lot about auto repair, you’ll need to pay a mechanic to perform the replacement job. That means you’ll need to pay both parts and labor costs.

The average replacement cost of an idle air control valve is between $120 and $500. The parts could cost anywhere from $45 to more than $400, while the labor is only around $70.

Of course, the labor cost really depends on the hourly rate of the mechanic. Since this job should not take more than 1 hour to perform, don’t expect the cost to be too high.

Certain vehicles are more complicated to work with than others, so that is a factor too.

11 thoughts on “5 Symptoms of a Bad Idle Air Control Valve (and Replacement Cost)”

1999-2005 Pontiac Grand Am has a screw to adjust idle speed. It is located on bottom side of the throttle body, and easiest to adjust if the throttle body is taken off. Has hex head, tighten to increase idle and loosen to reduce idle speed. I feel turning around 1.25 is good adjustment to test.

2004 heep liberty i belive the iac sensor is shot if you do not constantly give it throttle it will stall out. I removed it to see if is sticking but it seems fine. Could the electrical conection been the reaskn for this.

I found one for $11 so it pays to search online

Where online did you come across that great deal may I ask?

Could a bad transmission cause your cars rpm needle go crazy when idling I drive a 2002 Cadillac Seville. I don’t have 4000 for a new trans. I,m being told that is the problem. Any ideas welcome

Hi Carol, I would get a second opinion from another mechanic. If your transmission is behaving fine (no jerking, engine speed matches ground speed, etc) you could simply have a bad tach sensor or instrument cluster.

Take off your egr valve, emission gas regulator, if it is clogged up and the cars vacuum cant actuate the diaphragm inside it, it will cause the rough sporadic idle you describe and ultimately effect the transmission, by leading to a clogged catalytic converter, that causes extreme loss in power as the vehicle cant release the exhaust causing back pressure. If you are not racing the transmission not slamming it into park drive reverse i highly doubt it is the transmission. A bad transmission issue would be shift solenoids or maybe cracked torque converter, that would just cause the engine to stall immediately as you put it into reverse or drive if you are in park or neutral and still having idle issues it is not transmission related as the motor is not engaged to the transmission. The egr can be cleaned out with a degreaser and suck on the vacuum port to see if the diaphragm compresses, if it doesn’t or feels like you’re sucking through a straw the diaphragm is bad, replace the egr valve 60-100$ fix if the idle improves but still have lack in power loosen the exhaust at the headers, not muck just enough to allow the exhaust to bypass cats. If driving performance improves you have clogged cats, depending on the car you may have up to 3 example, a v6 or v8 has 2 exhaust headers therefore 2 upstream cats and 1 downstream unless you have dual exhaust then you have 4, 2 upstream and 2 downstream on a 4 cylinder motor has 2, 1 up and 1 down, catalytic converters are not cheap and most often require a muffler shop to install new ones. Simple test take an old rag and cup the tail pipe if it blows your hand off after a few seconds you cats are functioning properly if not odds are one or both are clogged. My bet is on that pesky EGR valve. The only other thing i can think of that would cause a sporadic idle is the Idle Air control valve, this one is activated by electronic solenoid that is governed by your vehicles temperature sending unit these two components work in conjunction with the throttle position sensor ignition timing etc. The IAC can be checked with a volt meter you would have to look up your vehicles operating parameters and use the volt meter to check for abnormal readings, good indication of bad IAC. So in a nut shell you got EGR, IAC, temperature sending unit, not the temp sensor, they are completely different, one shows the temp on your dash the other sends info to the computer why its calls a temp sending unit, because it sends data to the computer.

Absolutrly check your throttle body sensors FIRST…far cheaper to replace. A bad throttle body sensor offsets the air/fuel mixture and causes numerous problems, including idle surging. These sensors are IAC (appr. $75), the TPS…throttle position sensor (appr. $30), and MAP sensor …manifold absolute pressure sensor (appr. $30). You can buy an inexpensive obd2 scanner to read you codes… Or Autozone reads them for free.

I have 2002 Ford tours an it stalls out sometimes when I turn it off an start it back up it runs rough an want even pull out. After sitting for bout 10 minutes or so it starts up an runs find. Could this b a idle air control valve.

Mine takes bout 10 sec to start! Runs perfect then if sets few hours it does this! I cleans the I A C and M A F
Any ideas 98 Ford v6 c3.8

I’d start with the simple stuff. If your vehicle also cranks slow, I’d have the battery and alternator tested to make sure they are good.

How To Clean The Idle Air Control Iac Valve mp3


Длительность: 10 мин и 49 сек

Битрейт: 192 Kbps

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