Idle Speed - Installing Harness and Resistor

TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS

DATE: December 1986 REF..NO. MBNA 07.3/5


SUBJECT: A. INSTALLATION OF AUXILIARY WIRING HARNESS TO RAISE IDLE SPEED WITH TRANSMISSION ENGAGED. MODEL 201.024 MODEL YEAR 1986 ONLY

B. INSTALLATION OF 470 OHM RESISTOR AT COOLANT TEMPERATURE SENSOR TO IMPROVE THROTTLE RESPONSE DURING ENGINE WARM-UP PHASE. MODEL 201.024 MODEL YEARS 1984 AND 1985


In case of complaints about engine shaking when engaging the transmission or poor acceleration when the engine is cold, the service measures listed below can be performed to remedy the situtation.

FIGURE 1 - INSTALLATION OF AUXILIARY WIRING HARNESS:

Procedure

A. Installation of Auxiliary Wiring Harness to Raise Idle Speed With Transmission Engaged.

1. Remove left front carpet mat, lower instrument panel cover (remove knee bolster on vehicles equipped with SRS), side panel with integrated footrest and engine hood release (arrows, Figure 1).

2. Remove exterior lamp switch.

FIGURE 2 - DISCONNECT PLUG OF ENGINE WIRING HARNESS:

3. Disconnect plug of engine wiring harness (arrow) (brown/violet, black wires) in driver's footwell (figure 2).

FIGURE 3 - ATTACH CONNECTORS:

4. Attach connectors (a) from auxiliary wiring harness to respective engine wiring harness connectors and fasten with cable straps (Figure 3).

FIGURE 4 - SECURE MAIN GROUND:

5. Loosen left screw (arrow) from main ground (behind instrument cluster). The screw is located immediately behind the opening for the exterior lamp switch (Figure 4).

6. Route ground wire (0.5 mm dia., brown) to main ground screw behind instrument cluster (arrow), attach wire and retighten screw (Figure 4).
7. Reinstall exterior lamp switch.

8. Reinstall side panel with integrated footrest, engine hood release, lower instrument panel cover and carpet mat.
9. Check function. With engine oil temperature between 60~-80~C, the decrease in engine rpm when the shift lever is changed from "P"/"N" to any driving position, should not be more than 50 rpm.

FIGURE 5 - UNPLUG CONNECTOR AT COOLANT TEMPERATURE SENSOR:

B. Installation of 470 Ohm Resistor at Coolant Temperature Sensor to Improve Throttle Response During Engine Warm-Up Phase

1. Unplug connector (0.75 mm dia., green/red) at coolant temperature sensor (B11/2) (Figure 5).

FIGURE 6 - CONNECT 470 OHM RESISTOR IN SERIES:

2. Connect 470 Ohm resistor in series (arrow) between unplugged connector and temperature sensor (Figure 6).
3. Check on-off ratio and idle rpm. See Service Microfiche Engine 102 Combustion IIIa Job No. 07.3-106.
Parts Information

Part Name Part Number


Auxiliary Wiring Harness 201 540 78 34
Cable strap 001 997 42 90
470 Ohm resistor 201 540 80 34
Time Allowance

02-0219/41 Auxiliary Wiring harness (Idle speed), install 1.3 hrs.
02-0220/41 Auxiliary Wiring harness (Idle speed), install 1.0 hrs.
(with maint. or repair work)

02-0221/41 470 Ohm Resistor (Warm-up response), install 0.3 hrs.
02-0222/41 470 Ohm Resistor (Warm-up response), install 0.1 hrs.
(with maint. or repair work)