Figure 15.32. Idle speed compensation system diagram (1986 and 1987 models): 1 – atmospheric pressure sensor; 2 – intake air temperature sensor; 3 – coolant temperature sensor; 4 – ignition switch; 5 – air conditioning switch; 6 – air conditioner relay
The idle speed compensation system is designed to automatically increase the crankshaft speed, which decreases under the effect of additional load from the air conditioning drive and/or power steering at low vehicle speeds, when operating in high altitude areas or in hot climates. The idle speed is increased by increasing the air flow into the intake manifold through the bypass solenoid valves activated by the control unit, as well as from the air conditioning and power steering switches. In addition, the control unit also receives signals from the atmospheric pressure sensor, the coolant temperature sensor and the engine intake air temperature sensor. Based on this data, the control unit issues a command to open the specified valves (figure 15.32).
Before adjusting the bypass valves, the idle speed of the crankshaft should be determined and adjusted if necessary.
Figure 15.33. Idle Speed Compensation System Bypass Valve Connector Contact Location
Connect the tachometer. When the bypass valve connector is disconnected, apply a voltage of 12 V from the battery to the "WAT" contact, connect the "GRD" contact to the "ground" (figure 15.33). Check contacts in pairs. Compare the obtained rotation speed with the values given in the table. 15.8.
Table 15.8. Engine crankshaft speed when voltage is applied to contacts "BAT" and "GRD"
Check the idle speed for all valves. If the idle speed differs from the required one, adjust the valves by turning the screws.
Measure the resistance of each valve. If the resistance of any valve differs from the values given in the table. 15.9, replace the valve.
Table 15.9. Idle Speed Compensation System Bypass Valve Resistance for 1986 and 1987 Models
Figure 15.34. Using a voltmeter to check the idle speed compensation signals at the load compensation solenoid valve when the air conditioner or power steering is turned on
To check the air conditioner on signal that controls the bypass valve, warm up the engine to operating temperature and between contact "A" (in the bypass solenoid valve connector) and connect the voltmeter to the ground (figure 15.34). Turn on the air conditioner and fan, check the voltmeter reading, which should be equal to the battery voltage. If the reading is different, check the A/C relay and switch, A/C motor switch, fuses and wires.
To check the power steering signal that controls the bypass valve, connect a voltmeter between terminal "D" and ground. Have an assistant turn the steering wheel fully left and right; monitor the voltmeter readings, which should be zero.
If the readings differ, check the power steering switch and wires.
To test the high altitude compensation control signal, warm up the engine and let it idle. Connect a vacuum pump to the input port of the atmospheric pressure sensor, and connect a voltmeter to contacts "B" and "F". When a vacuum is created, the voltmeter should show zero. When the vacuum is removed, the reading should be equal to the battery voltage. If the readings differ, check the atmospheric pressure sensor and wires.
To test the compensation control signal in hot climates, warm up the engine and let it idle. Connect the voltmeter between the "TNA" contact of the intake air temperature sensor (installed in the air flow meter connector) and ground. Heat the sensor with a hair dryer to 55°C – the voltmeter reading should be zero. If the readings differ, check the intake air temperature sensor.