[W126 Coupe] MBCOUPES Digest, Vol 77, Issue 13 Cracked blocks and rough idle

[Henric]

Idle, the nemesis of every M117 owner.

The main components and causes for rough/inconsistent/high idle are:

1: Idle Control Module
2. Idle Control Valve
3. Vacuum loss/leak

Here's something I  posted years ago elsewhere:



The 116/117 does not have an adjustable idle control. Each component  
within the system that make up the idlecontrol must be functioning  
properly. Unless your vehicle was retrofitted with the old idle  
adjustment valve and ICV removed (pre-84), idle speed cannot be  
adjusted, only affected by failed componenets.

Here are the tests quoted from the MB sevice manual.

POOR IDLE

quote:
48hp - 3/4/2006 1:33 PM

Per Factory Service manual V-8 Engine 116..96 & 117.96:

Checking electric activation of idle spead adjuster (ICV)

Engine - operating temperature.
Ignition switched on.
Pull coupling from idle speed adjuster and measure voltage.

Readout approx. 12v then

Checking regulation of control unit

Engine at idle at operating temp. Plug on couple at idle speed  
adjuster in a manner that voltage can be measured on plug.

Readout 5v +-1 then

Check idle speed adjuster

Engine at idle.
Simulate coolant temp <42 degree C, for this purpose pull coupling  
from temp switch and bridge. (located at rear passenger side on top of  
manifold)

Idle speed increases to approx. 750/min.

End of test

Any other values then those described above suggest a faulty control  
unit (located at firewall)

If a faulty control unit is found, nowhere within the Mercedes Manual  
does it suggest this method but others have suggested this and it  
worked for me. Remove the control unit cover and lightly twisting from  
side to side while engine is running. Idle should drop to normal speed  
once twisted in a manner that effects the potential poor solder union.  
Heat each and every connection, adding a bit of solder to each point.  
My idle is now on the money.

Hope that helps.





On Nov 9, 2010, at 9:25 AM, Doug Gavin wrote:


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