Pic. 15.32. Diagram of the idle speed compensation system (1986 and 1987 models): 1 – atmospheric pressure sensor; 2 - intake air temperature sensor; 3 - coolant temperature sensor; 4 - ignition switch; 5 - air conditioner switch; 6 - air conditioner relay
The idle speed compensation system is designed to automatically increase the crankshaft speed, which decreases under the influence of additional load from the air conditioner drive and / or power steering at low vehicle speeds, when operating in highlands or in hot climates. The idle speed is increased by increasing the air flow to 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, coolant temperature sensor and engine intake air temperature sensor. Based on this data, the control unit issues a command to open the specified valves (pic. 15.32).
Before adjusting the bypass valves, determine the idle speed and adjust if necessary.
Pic. 15.33. The location of the contacts of the connector of the bypass valves of the idle speed compensation system
Connect a tachometer. With the bypass valve connector disconnected, apply to the contact «BAT» voltage 12 V from battery, contact «GRD» connect with «weight» (pic. 15.33). Check contacts in pairs. Compare the received speed with the values given in tab. 15.8.
Table 15.8. The frequency of rotation of the engine crankshaft when voltage is applied to the contacts «BAT» And «GRD»
Check 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 table. 15.9, replace the valve.
Table 15.9. 1986 and 1987 idle speed compensation bypass valve resistance
Pic. 15.34. Using a Voltmeter to Check Idle Speed Compensation Signals at the Load Compensation Solenoid Valve When A/C or Power Steering Is On
To test the A/C turn-on signal that controls the bypass valve, warm up the engine to operating temperature and between the «A» (in the connector of the bypass solenoid valve) And «weight» turn on the voltmeter (pic. 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 enable signal that controls the bypass valve, connect a voltmeter between the terminal «D» And «weight». Ask the assistant to turn the steering wheel all the way to the left and right; watch the voltmeter reading, which should be zero.
If readings are different, check the power steering switch and wires.
To check the compensation control signal in high altitude conditions, warm up the engine and leave it to idle. Connect the vacuum pump to the inlet fitting of the atmospheric pressure sensor, and to the contacts «IN» And «F» connect a voltmeter. When creating a vacuum, the voltmeter should show zero. When the vacuum is removed, the reading should be equal to the battery voltage. If the readings are different, check the barometric pressure sensor and wires.
To check the compensation control signal in hot climates, warm up the engine and let it idle. Turn on the voltmeter between the contact «TNA» intake air temperature sensor (installed in the air flow meter connector) And «weight». Heat the sensor with a hair dryer to a temperature of 55°C - the voltmeter reading should be zero. If readings are different, check the intake air temperature sensor.