[W126 Coupe] idle recurring "cough"

[Jay Hirsch]

On going minor problem since Sept 1

Car has  Bosch  rotor and distributor cap

Bosch factory  rotors.... made in Germany and Spain


This is what I did on Sept 2:

["Rotor was slightly burnt on one side, discolored, darker than rest  
of copper edge which is “normal.” But what is normal?
Showed it to a friend who is a very good auto mechanic.
      He said it looks  “a little more burnt than usual.” Told me to  
sand down that edge  to get the corrosion off
Put back dist. cap and with cleaned up rotor, car runs great, at idle  
and highway
Got new Bosch cap and rotor and will install later today]

One copper end of the rotor gets discolored...slighty burned or  
corroded.
Filed down  copper with 600 grit emory cloth.  Put back and all is  
fine, which I have done several times before which makes me think  
distributor is "out of balance

Factory coil and ignition  module.  Car has neve been "fooled with"

Have used my 1990  560 SEC  for a total of maybe 600 miles since Sept  
3.  Changed   rotor  and  dist cap at this time.
Car ran great...again

Went  about 250 miles  after Sept 3 when car started "coughing" at idle
Oct 4, changed spark plugs and rotor at this time, early   and car  
ran smooth..again

Have gone about 300 miles  since October., yesterday car started  
"coughing" at idle and not  running too smooth at speed also
Took out  rotor earlier today, installed new  rotor,  and  "presto"  
car is smooth and quick again.

Do you think  the distributor is out of balance and time for  
replacement?  car  just tuned 100,000 miles

or is there something else that is Mercedes related i am not aware  
of?  i  think it is just basic  "car problem," dist. getting tired.

Jay H

Had  the same  thing happen on two "gringo" cars of mine several  
years ago...1973 Eldorado and 1963 Lincoln out of balance distributors
They were "eating points"  when cars had points.  1973 was  last year  
for points on  Caddy's
Would change points, good for  a several  hundred miles and then  
"coughing and wheezing"

Changed distributors and no more problems
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