Tip & How-To about Mercedes-Benz E-Class

Idle Air Speed Control valve on engines


1.4) IACV Idle Air Control Valve - Idle Speed Control Unit(actuator)

What is it? The idle air control valve is an electrically driven mechanism that allows additional control over the throttle at idle.

Where is it located? The IACV is located on or near to the throttle body and consists of a small device with an electrical connector.

How does it work? When the throttle is closed the throttle plate closes offair from the inlet manifold and normally this would cause the engine to stall immediately. To allow the engine to keep running the ECU makes use of the IACV system to permit the ingress of a limited amount of air. The IACV device is seen in two forms either a) a small motor driven valve on a passageway allowing air indirectly to pass to the inlet manifold plenum or b) a motor located on theTPS assembly that opens the throttle plate by a small degree to allow air through directly. Both systems are designed to allow air to by-pass the 'closed' throttle plate to maintain engine idle. The IAC also helps throttle respond to additional power demands being made on the engine such as using the power steering, air conditioning or moving the (automatic) transmission selector into 'drive'. Somecar manufacturers also have a separate 'hot idle' valve system and this is designed to operate for a relatively short period just during engine warm up. Such hot idle systems are accompanied by electrically driven IAC valves to maintain engine idle in the face of additional power demands.

Symptoms of faulty IACV
Associated OBD2 error codesDTCs: P1508, P1509

  • Poor starting, sudden stall: If the IACV fails to open or the inlet/exit ports are clogged shut with oily deposits the engine may ignite and then promptly stall. The engine can be kept running by pressing the accelerator. However any additional demand on the engine such as power steering or putting the car into drive (automatic) will cause the engine to stumble badly or stall.
  • Engine stall at stop sign: Even with the engine is warmed up, if the car comes to a halt such as a stop light the engine may stall. The engine will often restart immediately with little trouble

Thisdiffers from:-
a) TPS fault - engine stall when theaccelerator is depressed quickly, but will often restart without much trouble.
b) CKP or CMP fault - engine cuts out without warning and is resistant torestart until cooled down

How to check? Physically remove the IACV, keep the electrical connection and examine the state of the valve for carbon build up. Blank off the exposed IACV port(s) on the throttle body and turn the engine on; you may have to give it extra throttle until the engine has warmed up. Monitor the IACV valve movement in response to additional loads (power steering inputs etc) the valve should open and close according to demand. When refitted this action results change in engine speed in response to increased power demand.

The electrical connector to the IACV can have 2 or 4 pins:-
2pins: resistance between socket pins should about 10 OHMS +/- 3 OHMS. If this resistance is very high then there is break and the IACV is at fault.
4pins: resistance between diagonally positioned pins should be about 20 OHMS. If the resistance is very high this indicates that the IACV is faulty.

Resistance between the actual metal valve body and either of the socket pins should be greater than 10,000 OHMS. If there is little or no resistance thenthere is a short and the IACV is faulty.

How to fix? If the motor of the IACV has failed (no movement and fault resistance values) then replace it. If the valve is gummed closed by baked oil and carbon then clean it thoroughly with WD40 or carburettor/choke cleaner spray and a cloth. Similarly if the entry and exit ports on the throttle body to the IACV look dirty again clean them out thoroughly.


NEXT 1.5) TAC Throttle Actuator Control

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What is an IAC Valve


Google is your friend in such questions.

  • Idle air control actuator - Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Idle_air_control_actuator An idle air control actuator or idle air control valve (IAC actuator/valve) ... Idle air control actuator; MAP sensor; Mass flow sensor; Oxygen sensor; Starter motor;
  • how to tell if your iac valve is going bad - YouTube www.youtube.com/watch?v=oNO8GCN8jQA
    • BY TIMMY102345
    • 6 MIN
    • 939K VIEWS
    2009-09-07 · Video embedded · how to tell if your iac valve is going bad timmy102345. ... #372 Better repair method Toyota Camry Idle Air Control Valve - ...
  • 4 Ways to Check an Idle Air Control Valve - wikiHow www.wikihow.com/Check-an-Idle-Air-Control-Valve
    • 525K VIEWS
    2015-12-11 · How to Check an Idle Air Control Valve. ... Again, an idle air control valve can have an issue or fault without triggering a check engine light. 2.


  • There are also videos in this link. How to check and fix.

  • What is an IAC Valve Bing video

    May 12, 2016 | 1992 Toyota Paseo

    1 Answer

    94 nissan altima won't start and iddle after cleaning IACV valve


    An IAC (idle air control) motor is designed to adjust the engine idle RPM speed by opening and closing an air bypass passage inside the throttle body. The cars computer or PCM (powertrain control module) receives information from various sensors and will output signals to adjust the idle air control motor in or out to adjust engine idle speed by controlling engine idle air. An idle air control motor can fail one of two ways, either the motor short circuits and stops working or the motor will develop high resistance and cause the idle air control motor to react slowly, either failure can cause the engine to stall at idle. When a trouble code scan is performed it sometimes won't always detect a failed or weak idle air control motor.

    Oct 08, 2012 | Nissan Altima Cars & Trucks

    2 Answers

    idle air control valve


    Any auto supply store will sell cleaners in spray cans for that purpose, also clean electrical contacts with electrical cleaner for that purpose, good luck

    Feb 17, 2012 | 1999 Ford Escort

    2 Answers

    idle fluxuates up and down consistantly


    Check the Idle Control System

    Idle speed is controlled by the Idle Air Control Valve (IACV). The IACV changes the amount of air being bypassed to the intake manifold, in response to electric current controlled by the ECM. When the IACV is activated, the valve opens to maintain proper idle speed.

    Symptom and Subsystems to Check:

    1. Difficult to start engine, when cold--check Fast Idle Thermo Valve.

    2. Fast idle out of spec, when cold:
    a. Check Fast Idle Thermo Valve.
    b. Check IACV.
    c. Check idle adjusting screw (see Section C).

    3. Rough idle:
    a. Check hoses and connections.
    b. Check IACV.

    4. RPM too high, when warm:
    a. Check IACV.
    b. Check Fast Idle Thermo Valve.
    c. Check hoses and connections, check Power Steering Pressure Switch Signal, and check idle adjusting screw.

    5. RPM too low, when warm:
    a. Idle speed is below specified rpm, with no load--check IACV and idle adjusting screw.
    b. Idle speed doesn't increase after initial start up--check IACV.
    c. Idle speed drops in gear (automatic transmission)--check automatic transaxle gear position switch signal.
    d. Idle speed drops when AC is on--check air conditioning signal and IACV.
    e. Idle speed drops when steering wheel is turned--check power steering pressure switch signal and IACV.
    f. Idle speed fluctuates with electrical load--check hoses and connections, IACV, and Alternator FR Signal.

    6. Frequent stalling, while warming up--check IACV and idle adjusting screw.

    7. Frequent stalling, after warming up--check idle adjusting screw and IACV.

    Additional Steps:

    . Check Alternator FR Signal. Have alternator inspected, if idle speed fluctuates with electrical load. The FR signal communicates to the ECM how "hard" the alternator is working to meet the electrical demands of the car, including the battery and any loads which aren't monitored by the ELD. This square-wave signal varies in pulse width, according to the load on the alternator. The ECM places, approximately, 5 reference volts on the wire. The voltage regulator will drop this signal to approximately 1.2 volts, in proportion to alternator load. The ECM compares the electrical load (ELD) signal with the FR (Charging Rate) signal from the alternator and uses that information to set the idle speed and turn the alternator on and off. This helps fuel economy.

    . Clean main ECM ground on thermostat housing.

    . Reset ECM, by removing the 7.5 amp Back Up Fuse, in the under-hood fuse box, for 10 seconds.

    . Replace PCV Valve, cleaning hose with brake cleaner spray.

    . Substitute a known-good ECM. If symptom goes away, replace original ECM.

    Check the ICM (Erratic RPM and PGM-FI System)

    When the engine is cold, the air conditioner compressor is on, the transmission is in gear (automatic transmission only) or the alternator is charging, the ECM controls current to the Idle Air Control (IAC) Valve to maintain correct idle speed. Here's an overview of how the PGM-FI System works.

    Background:

    Various inputs to the ECM are TDC/CKP/CYP Sensor, MAP Sensor, ECT Sensor, IAT Sensor, TP Sensor, HO2S, VSS, BARO Sensor, EGR Valve Lift Sensor, Starter Signal, Alternator FR Signal, Air Conditioning Signal, Automatic Transmission Shift Position Signal, Battery Voltage (Ignition 1) Brake Switch Signal, PSP Switch Signal, ELD, and VTEC Pressure Switch.

    Inputs are received and processed by the ECM's Fuel Injector Timing and Duration, Electronic Idle Control, Other Control Functions, Ignition Timing Control, and ECM Back-up Functions. These are the primary functional areas within the ECM.

    Outputs from the ECM control Fuel Injectors, PGM-FI Main Relay (Fuel Pump), MIL (Check Engine Light), Idle Air Control (IAC) Valve, A/C Compressor Clutch Relay, Ignition Control Module (ICM), EVAP Purge Control Solenoid Valve, HO2S Heater, EGR Control Solenoid Valve, Alternator, Lock-up Solenoid Valve A/B (A/T), VTEC Solenoid Valve, and Interlock Control Unit.

    Idle RPM:

    Once you understand how the PGM-FI system is configured, it's easy to see how the ECM, Idle Air Control Valve, and the Ignition Control Module affect idle rpm. If the ECM's Electronic Idle Control function is not working properly, then it cannot properly control the IAC Valve. Likewise, if the ECM's Ignition Timing Control function is not operating properly, it cannot properly control the ICM (igniter). Obviously, idle rpm will also be affected if there's a problem with the IAC Valve or the ICM. As stated above, the ECM controls current to the Idle Air Control (IAC) Valve to maintain correct idle speed. This cannot happen if the IAC Valve is failing. The same situation exists if the ICM is failing. The ECM will tell the ICM to open and close the primary voltage circuit going to the coil and it won't respond properly. The result will be erratic spark plug firing and erratic rpm.

    Conclusion:

    If you are experiencing erratic idle rpm, try and isolate whether the problem is caused by the ICM (ignitor), IAC Valve, or the ECM. My experience has been that a failing ICM is usually responsible for the problem. Keep in mind that tachometers are connected directly to the ICM. Therefore, a fluctuating tachometer needle is often a dead giveaway. Heat and poor preventive maintenance (causing high secondary voltage to be discharge on internal distributor components) frequently causes the ICM (and coil) to fail. Besides performance, this is another reason why it's important to regularly replace spark plugs, spark plug wires, rotors, and distributor caps. Electricity will always follow the path of least resistance, even if it isn't the intended one. Our job is to ensure the intended path is the path of least resistance.

    Ignitor (ICM) and Coil Replacement:

    1. Disconnect negative battery cable.
    2. Remove hex head machine screws, securing distributor cap to housing, using an 8 mm nut driver.
    3. Move distributor cap and wires off to the side.
    4. Remove machine screw securing rotor to shaft, using a #2 Phillips head screwdriver. It may be necessary to "hit" the starter once or twice, in order to rotate rotor for access to mounting screw.
    5. Remove rotor and leak cover.
    6. Unfasten ignitor wires, remove coil mounting screws, and set coil aside. Note: Removing coil first improves access to igniter.
    7. Unfasten screws securing igniter to housing.
    8. Remove ignitor from distributor and unfasten screws mounting ignitor to heat sink.
    9. Coat back of new ignitor (or old igniter, if reusing) and male connectors with silicone grease. Silicone grease increases heat transfer to heat sink. Failure to apply silicone grease will cause the ignitor to quickly fail.
    10. Mount ignitor to heat sink and reinstall ignitor, igniter terminal wires, coil, coil wires, leak cover, rotor, and distributor cap. Ensure female ignitor terminals fit snugly--crimp with pliers, if necessary.

    AutoZone can test ICMs and coils for free. If you plan to keep the car, I would replace the ICM due the age of your Civic.

    Sep 15, 2010 | 1991 Honda Civic

    1 Answer

    idling problem toyota altis


    Either there is a vacuum leak causing the high idle, or
    the IACV is bad or being controlled by the computer to make idle speed too high:

    To change the IACV refer to the following:
    Idle Speed Control (Idle Air Control) Valve Removal & Installation To Remove:
    1. Before servicing the vehicle, refer to the precautions in the beginning of this section.
    2. Remove the throttle body. Idle speed control valve toy_cor-04-18-1187.gif

    3. Remove the 3 mounting screws from the throttle body. Remove the idle speed control valve and gasket.
    To Install:
    1. Using a new gasket install the idle speed control valve on the throttle body with the 3 mounting screws.
      • Tighten 33 inch lbs. (3.7 Nm).
    2. Install the throttle body.
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    Jul 16, 2010 | 2004 Toyota Corolla

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