11.32 Idle control valve (ISCV)
The idle control valve is a DC motor that the electronic control unit can rotate either clockwise or counterclockwise. Rotation in one direction opens the valve and rotation in the opposite direction closes it.
Duty cycle can be measured on each ground circuit to determine when the valve opens or closes.
When additional power consumers are switched on, for example: headlights or a heater fan, the idling speed will decrease.
The normal idling speed must be maintained in all operating conditions of the engine: both on a cold and warm engine.
Idle air control valve voltage values (ISCV)
Terminal numbers
See illustrations 11.2, 11.3, 11.4, 11.5, 11.6
* Ignition on, the instrument must indicate the nominal voltage of the battery (nbv). With the engine running, the voltage will decrease, and as the load on the engine increases, the voltage will decrease further.
Idle Air Control Valve Resistance Values (ISCV)
Idle Air Control Valve Duty Cycle Table (ISCV)
Terminal | Frequency Hz | duty cycle % |
1 | 31 | |
3 | 69 |
Idle air control valve type (ISCV)
- Rotating
- Influence of external factors
- Basic throttle setting
- Vacuum leak
- Throttle sticking
- Poorly adjusted or stuck throttle cable
- Incorrect CO adjustment
- Incorrect ignition timing
- Ignition system malfunction
- Inaccurate signal from the coolant temperature sensor
Checking the idle control valve (ISCV) (general check)
1. Inspect the idle air control valve multi-pin connector for signs of corrosion or damage.
2. Make sure the connector terminal pins are properly installed and making good contact with the idle air control valve multi-pin connector.
3. Before diagnosing the idle control valve, check the following components.
Engine mechanical failure
- Incorrect ignition timing Incorrectly adjusted throttle
- Throttle position sensor incorrectly adjusted (TPS)
- Throttle body contaminated with soot
- Vacuum leak through induction valve
- Incorrect CO level
- Air filter clogged
Idle air control valve checks (ISCV)
1. Let the engine run at idle speed.
2. Make sure that the idle speed is within the nominal values.
3. Increase the load on the engine by turning on the headlights, rear window defroster and heater fan. The idle speed should change.
4. Quickly squeeze one of the air hoses. The idle speed should increase and then return to the nominal value.
5. If the idle speed is higher than the nominal values, then this does not indicate a malfunction.
Checking the performance of the ISCV valve using an oscilloscope, voltmeter, or meter for the duration of the closed state of the breaker contacts
1. Three wires are connected to the multi-pin connector of the idle control valve: a power wire and two signal wires.
2. Peel back the rubber insulation (where possible) to the WF1 multi-pin connector of the idle air control valve or connect an output block (WWII) between the multi-pin connector of the electronic control unit and the electronic control unit.
3. Connect the negative lead of an oscilloscope, voltmeter, or breaker closed duration meter to ground on the motor.
4. Connect the positive lead of an oscilloscope, voltmeter, or breaker open time meter to one of the idle control valve signal wire terminals.
5. The engine is running. The instrument should show a square wave, AC voltage or duty cycle according to the values specified in the specifications (see illustration 11.33).
11.33 Typical waveform of the idle control valve signal from the electronic control unit
Note. The digital voltmeter will show the average voltage.
6. Increase the load on the engine by turning on the headlights, rear defroster and heater fan. The average voltage and duty cycle will change. The pulse frequency must remain constant.
No waveform or idle control valve signal
1. Turn on the ignition and check for battery voltage at the power wire terminal.
2. If there is no voltage, trace the wiring back to the appropriate terminal of the electronic control unit.
3. Check up presence of conductivity of wires between the valve of management of idling and plugs of the electronic block of management.
Accurate signal, but the idle speed does not correspond to the nominal values
1. Disconnect the multi-pin connector of the idle control valve.
2. Check the resistance between the indicated terminals.
Note. Make the following connections very quickly.
3. Using a jumper wire, connect the battery to one of the idle control valve power wire terminals.
4. Using a second jumper wire, connect the idle control valve switch wire terminal to ground. The idle control valve should work.
5. Move the second jumper wire to connect the other idle control valve terminal to ground. The idle control valve should work in reverse.
6. If the idle control valve does not actuate or its efficiency is reduced, then the idle control valve may be defective.