W124 OM606 engine running issue

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Charles Morgan

MB Enthusiast
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Feb 2, 2010
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Mercedes 250CE W114, Alfa Romeo GT Coupe 3.2 V6
An intriguing one. I have a W124 multivalve (OM606) diesel estate on my drive which finally I want to get back on the road. A couple of years ago I took off the manifold to get to the glowplugs to replace them, of which I managed 5 of 6. I never got round to putting the manifold back on, but last weekend a mechanic friend did so for me. Now when it fires up, it idles at about 1400 rpm and then goes full tilt to about 4000 rpm without me touching the throttle.

What might be causing this?
 
Most of these diesel mechanical pumps have a centrifugal regulator or governor to prevent diesel runaway. It sounds as if this is sticking possibly due to non use? These mechanical pumps are marvelous little "engines" in their own right but require expert fettling. There may be ways to flush it clean if sticky deposits have formed not sure
this video of an older pump will give some idea of the complexity! the governor makes an appearance at about 32 minutes in
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This is the guy you need Charles -the legendary Dieselmeken!
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It's entirely possible a number of things went awry on refitting. I'll have a good look at those links thanks!
 
Did you jump start the car? If so check the OVP relay/ fuse ---- the electronic idle control and many of the vacuum valves are supplied by the OVP relay
 
No jump start, battery was fully trickle charged. The OVP relay was changed about 18months ago for something that worked. The loom, it must be said, is in lousy condition. That includes the glowplug leads to the relay (irrelevant here) and the wiring to the manifold. I normally move the car several times a year without the manifold on and no problem. So my assumption to start with is something went awry when that was put back on.
 
Sorted - the idle adjustment of the throttle cable was so far out the engine was racing. Now set to a very comfortable idle.
 

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