[W126 Coupe] swapping idle speed controllers?

[Dick Spellman]

For what it is worth below is a snip from a posting I did back in 2005.  
Plus I will add that you should NOT install a new or remanufactured idle 
speed controller without first confirming the over voltage protection 
relay (OVP) is working properly.  If in doubt, replace it first or you 
end up with a damaged idle speed controller in short order that will be 
'out of warranty' for failure to affirm the OVP is in fact working as it 
should.  Pricing is around $150 US with a core charge. 

"Just thought I mention that the remanufactured idle speed control 
showed up with simple 1 page instructions that included:
proper resistance values at the idle speed adjuster terminals that were 
as follows:
  a.. European models from 1981 and other models from 1986 (3.5 - 4.5) ohms
  b.. All other models 1981 - 1985 (8-12) ohms
Where I have the 1983 380SEC the value I read using a digital volt ohm 
meter (DVOM) BEFORE installing the new Idle Speed Control was 10.1 ohms 
which was just about dead center in the range the benz-store provided in 
their instructions for the idle speed adjuster.

One other neat little 'tweak' that is a part of the remanufactured unit 
is and was not on the original part is a fine tuning adjustment screw 
that gives you the ability to really get your idle to exact spec with ease.

New part installed, air slider hoses replaced, air slider cleaned (per 
Mike Ramay) all other sensors in spec and the car purr's as it should 
with no hint of a miss or stumble.

The benz-store provided UPS tracking #, good packing, installation 
instructions, core return card, 3 year warranty and overall I'd give 
them an A+++ for service and super instructions. I am on to repairing 
(2) cruise controls next with the benz-store providing the rebuilt 
amplifiers.

Regards,

Dick

btw: my unit specific to the 83 380 engine was clearly cross-referenced 
on the sealed box and on the sealed unit as part #002 545 33 32 (they 
add an 88 to the end which I presume means they remanufactured and added 
the cool idle adjustment screw)

Description of parts: For those that don't know about the idle speed 
adjuster, it's the small cylinder about 1/2 the diameter of a soda can 
set horizontal on the engine with a single plug 2-wire hook-up on the 
front and two 3/4 inch or so diameter hoses just pressed on the back. 
And for those curious about the description of the Idle Speed Control, 
it's a black box about 4 inches square and about 3/4 inch thick. Mine 
was conveniently located on the electrics firewall about the center of 
the engine bay with one plug in harness and one 10mm screw holding it in 
place. "