Carburetor, fuel pump, throttle linkage,  M110

Adjusting idle speed



07.2-100 Adjusting idle speed


Identification: Information plate in national language on cross member in front of radiator or on cylinder head cover. Adjust engines according to data of respective emission control information plate.


Testing and adjusting values


National version
Idle speed 1/min
Idle speed emission value % CO


up to 1976
max. 1.5


max. 1.0 without air injection






up to 1.5


(us*) 1974 Federal


1974 California
6—8 without air injection


max. 1.0 without air injection


Vacuum governor1)


National version
Engine speed
Vacuum hose pulled off
Engine speed
Driving position engaged


TN choke
TN choke








(usa) 1973/74




‘) When engaging all auxiliary units, the engine should still run smoothly.


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Special tools


Oil telethermometer
m110 - 0270-1.jpg
116 589 27 21 00


Digital tester
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001 589 54 21 00


Connecting cabie 6 m long
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000 589 04 90 00


Intermediate plug (adaptor)
m110 - 0270-4.jpg
000 589 72 63 00


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000 589 71 63 00


Conventional tools


Rpm and CO measuring instrument




Do not set idle speed on dynamometer when the engine is too hot, e.g. immediately after a fast drive or after measuring output. The air filter must be mounted.


m110 - 0270-6.jpg
1    Connect test instruments:
•   digital tester or revolution counter
•   CO measuring instrument
•   oil telethermometer
2   Switch off air conditioning system or automatic climate control. Move selector lever into position “?”.


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3   Check whether on vehicles with cruise control (Tempomat) the Bowden wire rests free of tension against regulating lever. Adjust Bowden wire with adjusting nut (1), if required. For this purpose, run engine.
4   Set engine oil temperature to 60—80 °C.
5   Check intake system for leaks. For this purpose, spray all sealed points with Iso-Oktan DIN 51 756 or benzine. A changing engine speed or CO value indi­cates the presence of leaks.
Do not use conventional fuel for spraying (unhealthy vapors). Pay attention to inflammability and do not spray on the red-hot parts or components of the igni­tion system.
m110 - 0271-1.jpg
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6   With the engine running, check whether throttle valve lever (3) rests against adjusting screw (68).
7   Check idle speed and adjust with adjusting screw (68), if required.
m110 - 0271-3.jpg


8 Check idle speed emission value without air injec­tion. For this purpose, make air injection inoperative as follows (for (@) 1973/74 nothing need be made inoperative):
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CD 1976
Pull off blue/purple vacuum line at connecting point (arrow).


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V) 1976, model 114
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Pull rubber cap (arrow) from blue/purple vacuum line.


j[) 1976, model 116
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Pull rubber cap (arrow) from blue/purple vacuum line.


(us*) California 1974
Pull off red vacuum line at connecting point (arrow). @) 1975/76
Pull off blue/purple vacuum line at connecting point (arrow).
m110 - 0272-3.jpg


The exhaust gas for idle speed CO measurement on vehicles with catalyst, (T) 1976 and (usa) 1975/76, is drawn off in front of catalyst at check valve (arrow) of air injection.
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For measuring idle speed emissions, open valve plate of check valve by means of a self-made wire hook. Connect exhaust gas hose of CO measuring instrument to check valve.
m110 - 0273-1.jpg


9 Adjust idle speed emission value without air injec­tion. For this purpose, adjust both adjusting screws (arrows) uniformly.
Screwing out = richer Screwing in = leaner
Accelerate for a short moment, check idle speed and idle speed emission value once again and readjust, if required.
m110 - 0273-2.jpg


10    Reattach vacuum hose for air injection (air injec­tion operating). The idle speed emission value should now be below the previously set value.
11    Adjust vacuum governor. Run engine, pull off vacuum hose (64), set to specified speed by means of an adjusting screw (63), attach vacuum hose.
When loosening counternut, apply counterhold to diaphragm rod.
Engage driving position on automatic transmission, set to specified speed by means of adjusting nut (61). Turn power steering to full lock and engage air condi­tioning system, engine should still run smoothly. Readjust speed, if required.
m110 - 0273-3.jpg


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