[W126 Coupe] 560 frustrations

[Stephen .]

I am trying to prepare my '88 560SEL for the road for the winter (and 380SEC 
back into storage by November) but have a couple of major issues in need if 
help/advice/experience.

The engine starts, and runs, albeit at a tad too high idle (1200RPM up and 
down +/- 200).  It does not drop to warm idle even when the temp gauge shows 
running temperature.  The engine does not overheat but as normal,  warms up 
quickly and stays steady at about 80C.

Then after about 10 minutes of running, the engine shuts down with no spark 
just as though I turned the key off.  The fuel system functions OK.  After 1 
hour cooling down there is still no spark.  After two hours the engine 
starts again and the situation repeats.

The ignition module is OK.  (switched with a known good one with the same 
result)

The ignition components (cap, rotor and wires) all could stand being 
replaced but obviously do not prevent the engine from running.  This leaves 
the coil suspect.  Has anyone had a coil behave (mis-behave?) in this 
matter?

Question:  How do you test the coil if the operation is intermittent?  (OR 
does anyone have a used coil I can buy to switch out?)

I intend to solve the idle problem once I can solve the ignition problem.  I 
suspect air leakage past the idle control valve hoses, crud buildup in the 
intake or the valve itself, possible vacuum problem, and possibly a 
defective idle control module, but troubleshooting that is difficult when 
the damn thing won't run for longer than 10 minutes.

Next Question will be: WHERE is the ignition control module??

Appreciate any help...
Stephen .

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