[W126 Coupe] rough idle

[Jonathan]

Tim Graney wrote:

> Here is a question for all you guru's out there. I have a 1985 500SEC 

> Euro AMG which I have pretty much replaced every top part on the 

> engine and it still idles rough when it is cold . I replace all the 

> elements that control the idle. The box, the valve, the fuel 

> controller, warm up regulator. It starts right up and idles to around 

> 850 RPM nice and smooth then starts to stumble a little bit like it is 

> running fat. It runs fine once you take off but stumbles a bit unitl 

> it reaches operating temp. As soon as it reaches 80C it smooths out 

> and runs and idles perfectly at 500RPM. I replaced all the sensors on 

> the motor. The only two I have not replaced are the two thermo time 

> switches. I also did the heads and replaced all the hydraulic 

> compensators and lash caps along with all new valves and springs. I 

> just cleaned the the surface of the heads about .002 to give a nice 

> mating surface. All the wires have been replaced. New Cap, New Rotor. 

> I have adjusted the fuel mixture ad nauseum. I use a vacuum gauge and 

> a exhaust gas analyzer and like I said it run tits when warm but crap 

> when cold. Any Ideas?

> ------------------------------------------------------------------------

>

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I didn't notice injectors in the above list..

When you say fuel controller, do you mean the regulator or the fuel 
distributor?

What spark plugs are you running?  Did you check the wires to be Sure 
they're spot on (anything beyond 1.2-1.3 Kohms I consider bad).

I would go ahead and replace those thermo time switches, they're cheap 
and easy.

Has this car been federalized (I'm assuming you are in country).  
Sometimes they install O2 sensors and frequency valves and once they 
fail can lead to issues.

Jonathan


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1996 S600 Euro "Scharnhorst"
1991 560 SEC Full Euro ECE (for sale)
1991 560 SEC 226Hp/271ft/lbs (TT conversion IP)
1988 300 TE
1989 560 SEC AMG (Mech.lifter/radical cam conv.)
1986 560 SEL 6.0L 32V AMG
1980 280 SE Euro
2006 Z4 3.0Si M-Spec

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