Engine - Idle Speed Control System Description
Group 11Engine
Bulletin Number
11 02 82 (2009)
Montvale, NJ
September, 1982
Technical Dept.
This bulletin supercedes Technical Reference 11 12 82 (2008) which contained an error in wiring color code (page 3, # 6). Please remove bulletin 11 12 82 (2008) and discard.
Subject:
IDLE SPEED CONTROL SYSTEM - 528e, 633CSi, 733i
An electronically regulated idle speed control system was introduced with the 1982 model year 528e, 633CSI, and 733i in conjunction with the Motronic system. The idle speed control system allowed for a lowering of engine idle speeds.
The system consists of:
Idle Control Unit Coolant Temperature Switch
Idle Control Valve Air Conditioner Switch
Air Temperature Sensor Automatic Transmission Switch
The idle control unit regulates the cross sectional opening of the idle control valve in response to any deviation in speed. By opening and closing the valve, bypass air (measured by the Air Flow Meter) is supplied to the engine in the quantity required for idle operation.
The measurable variables supplied to the idle control unit are:
1. Engine Coolant Temperature
2. Engine Speed
3. Outside Air Temperature
4. Air Conditioner Switch ("off" or "on")
5. Automatic Transmission Selector Switch (P or N)
6. Throttle position ("closed" or "open")
Three different idle speeds (nominal speed) can be maintained by the idle control system:
Automatic Transmission
1) In drive, 1 or 2 700 RPM
2) Park or Neutral
a) engine cold (below 45°) 950 RPM
b) engine warm (above 45° C)
i) ambient air temp. (less than -5 C) 850 RPM
ii) ambient air temp. (greater than -5 C)
-A/C on 850 RPM
-A/C off 700 RPM
Manual Transmission
1) Engine cold (below 45° C) 950 RPM
2) Engine warm (above 45° C)
a) ambient air temp. (below -5° C) 850 RPM
b) ambient air temp. (below -5° C)
-A/C on 850 RPM
-A/C off 700 RPM
The idle control unit regulates air flow through the idle valve by varying the electrical current supply to the valve. The higher the current to the valve, the less air flow through it. The lower the current to the valve, the higher the air flow through it. For example:
A. Engine at idle (700 RPM) , approximately 480 milliamp. Current at valve
B. Engine at idle with A/C on (850 RPM), approximately 480 milliamp. Current at valve
In condition "B", more air flow is required to maintain 850 RPM, and the current to the valve is lowered accordingly.
Recalibration of Throttle Set Screw After Major Engine Repairs:
1. Engine at operating temperature.
2. Transmission in neutral (or "park" on automatic).
3. Air conditioner switch - "off".
4. Stop engine.
5. Connect multimeter "in series" with idle control valve (plastic plug at valve will unsnap for easier access to wire connectors). Set multimeter to read DC (Direct Current) amperes.
6. Disconnect plug connector from throttle butterfly switch. Jump wires # 2 and # 18 in plug connector (brown and brown/blue). This insures a "closed throttle" signal to the idle control unit.
7. Start engine. At 700 RPM, the current measured at the idle control valve should be 470 to 490 milliamps.
If the measured current is less than 470 milliamps, the amount of air flow through the throttle housing should be increased as shown:
a. Turn the throttle set screw in (opening the throttle) while observing the idle valve current. Stop when the measured current reaches the desired value of 470 - 490 milliamperes. Tighten the lock nut on the set screw.
b. Stop the engine and check the throttle butterfly switch "closed" contacts. If necessary, adjust the throttle butterfly switch.
8. Remove the "jumper" from the throttle butterfly switch plug and reconnect the plug to the switch.
9. Start engine and accelerate several times from idle to about 1500 RPM, to verify that the desired value of 470-490 milliamps is obtained each time the engine returns to idle.
10. Stop engine, disconnect multimeter, and reconnect plug to idle control valve.
WARRANTY STATUS
Recalibration of throttle set screw - FRU: 4