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Idle Speed Control System Volvo 240 I

Testing & Diagnostics 3 illustrations ~1074 words

DESCRIPTION

Gasoline models are equipped with an electronic idle speed control system which maintains a constant idle speed under all conditions. The control unit monitors engine speed and actuates an air control valve which by-passes throttle valve and increases or decreases the amount of air to engine.

This air supply is varied to maintain idle speed. System includes the control unit, air control valve, throttle switch, coolant sensor, A/C switch and connecting wiring and hoses.

OPERATION

The constant idle speed system controls an air control valve which by-passes additional air around the air flow throttle valve. Idle speed is maintained by the amount of air injected into the intake manifold, behind the air flow throttle valve. System components operate as follows

ELECTRONIC CONTROL UNIT

The electronic control unit processes information received from the engine coolant temperature sensor, throttle switch and distributor. After receiving information on coolant temperature, throttle position and engine speed, the control unit sends electrical impulses to the air control valve to regulate idle speed.

Fig. 1: Electronic Idle Speed Control System (V6 & 4-Cylinder Turbo Shown)
Scheme 1: Electronic Idle Speed Control System (V6 & 4-Cylinder Turbo Shown)

AIR CONTROL VALVE

The air control valve consists of a small electric motor mounted between connecting hoses at the air flow throttle valve. The electric motor rotates clockwise or counterclockwise, depending on electrical signals received from the electronic control unit.

The control valve is rotated to increase or decrease the amount of air which is taken from in front of the throttle valve, by-passed around the throttle valve and injected into the intake manifold, behind the throttle valve.

THROTTLE SWITCH

The throttle switch is a small electrical switch which is activated by the throttle lever to inform the electronic control unit when the throttle valve is at the idle position. On V6 engines, the electrical circuit between the throttle switch and electronic control unit is closed at idle position. On all other engines, the ground circuit between the throttle switch and electronic control unit is interrupted at idle position.

COOLANT TEMPERATURE SENSOR

The coolant temperature sensor provides an electrical impulse to the electronic control unit at low coolant temperatures. At low temperatures, the electronic control unit activates the air control valve to provide more air to increase the engine speed.

A/C SWITCH

When the air conditioner is activated, the control unit increases idle speed to compensate for the additional load caused by the air conditioning system.

IGNITION COIL

Terminal 1 on the ignition coil is connected to the electronic control unit to provide it with engine speed information.

4-Cylinder Non-Turbo Vehicles

  1. Connect ohmmeter between ground and terminal "3". Depress accelerator pedal. Meter should show zero resistance in idle position and infinite resistance in other positions.
  2. Connect ohmmeter between ground and terminal "12". Depress accelerator pedal. Meter should show zero resistance in full throttle position and infinite resistance in other positions.
  3. If incorrect, check throttle valve switch ground at intake manifold. If ground connection is okay replace throttle valve switch.

4-Cylinder Turbo Vehicles

  1. To test throttle switch circuitry, connect voltmeter across terminals "1" and "2". With ignition on and engine stopped, voltmeter reading at idle should be 2-8 volts.
  2. Above idle position, voltmeter reading should be 0 volts. If throttle switch does not respond as outlined, go to next step.
  3. With voltmeter still connected, ignition on and engine stopped, insert feeler gauge (Scheme 1)
  4. Using feeler gauge listed in Throttle Switch Voltage Reading chart should produce voltages indicated in chart. If not, replace throttle switch and go to next step.
  5. After replacing throttle switch, connect voltmeter and turn ignition on with engine stopped. Loosen lock nut and turn adjusting screw on throttle lever until meter reading drops to 0 volts. Tighten lock nut.
  6. Insert.016" (0.4 mm) feeler gauge. Loosen throttle switch retaining screws until reading is indicated on voltmeter. Tighten retaining screws.
ApplicationFeeler Gauge: In. (mm)Voltmeter Reading
4-Cyl. Turbo.008 (0.2)Any
4-Cyl. Turbo.045 (1.1)0 Volts

4-CYL TURBO THROTTLE SWITCH VOLTAGE SPECIFICATIONS

Testing Throttle Switch Operation (4-Cyl Turbo). Scheme 1

Scheme 1: Testing Throttle Switch Operation (4-Cyl Turbo)
Scheme 1: Testing Throttle Switch Operation (4-Cyl Turbo)

V6 Vehicles

  1. Connect a test lamp between micro-switch yellow wire and 12V current supply.
  2. Check that switch closes (test lamp lights).04-.1" (1-2.5 mm) before throttle control pulley touches full throttle stop. (Scheme 2) Adjust if required.

Testing Throttle Switch Operation (V6). Scheme 2

Scheme 2: Testing Throttle Switch Operation (V6)
Scheme 2: Testing Throttle Switch Operation (V6)

AIR CONTROL VALVE (ACV) TEST

Note. The following test is for models with separate Idle Speed Control only. For models with integral fuel injection and idle speed control systems, see FUEL INJ - BOSCH LH article in the FUEL SYSTEMS section.

  1. Disconnect ACV harness connector. Measure resistance between terminals 3 and 4 and between terminals 4 and 5. Resistance should be about 20 ohms.
  2. Warm engine to operating temperature. Ground the Blue/White ACV test connector (located near the coil). ACV valve will close and engine speed should drop to about 600-650 RPM.

COOLANT TEMPERATURE SENSOR (CTS) TEST

Note. The following test is for models with separate Idle Speed Control only. For models with integral fuel injection and idle speed control systems, see FUEL INJ - BOSCH LH article in the FUEL SYSTEMS section.

Measure resistance between CTS sensor terminals. Resistance for 4-cylinder engines at 68°F (20°C) should be 2100-2900 ohms and 270-390 ohms at 176°F (80°C). Resistance for V6 engines at 68°F (20°C) should be 8500-11500 ohms and 770-1320 ohms at 176°F (80°C).

ECU CIRCUIT TESTS

Note. The following test is for models with separate Idle Speed Control only. For models with integral fuel injection and idle speed control systems, see FUEL INJ - BOSCH LH article in the FUEL SYSTEMS section.

  1. Locate ECU at right kick panel. Unplug both ECU harness connectors. Turn ignition on. Ensure 12 volts are present at terminal No. 1. Ensure terminal No. 2 has continuity to ground.
  2. Connect a tachometer between terminal No. 12 and ground. Start engine. Tachometer should indicate engine RPM.
  3. Some models with A/C have a White/Green or Red wire attached to terminal No. 7. If so, turn A/C on and ensure there are 12 volts present at terminal No. 7. NOTE: During A/C operation, the engine speed should increase about 150 RPM.
  4. Using jumper wires, connect one jumper wire between terminals No. 1 and 4. Connect another jumper wire between terminals No. 2 and 5. Start engine. If engine speed increases to 1600-2400 RPM, the ACV is okay. If not, check wiring and ACV.
  5. Repair or replace any defective components or circuits. Remove jumper wires. Connect all harness connectors. Check to see if idle speed control system is working. If not, ensure all connectors are clean and tight. If no problems are found, but idle speed control system is still working incorrectly, replace the ECU.

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