560SEC Lumpy idle

[steveb]

I have recently bought 560SEC & notice that the idle is 'lumpy' & I suspect dropping a couple of cylinders. The idle speed seems even at about 600rpm, but does not feel smooth in the car, & when I pull away is a little hesitant & sounds uneven for a second or so.

I have not yet checked the 'usual suspects' (plugs, dist. cap etc.) but is there anything in particular that I would otherwise be unfamiliar with? Car has been regularly serviced, full top-end recon at 95K, now 105k.

Hope you can help

Steve

 

[mercmush]

My 560SEL had a lumpy idle problem when I first bought it that also manifested itself with a misfiring engine and really shabby mpg. It was painlessly cured by replacing 2 spark plugs.

 

[steveb]

Hoad a good lok around & it seems like kn@ckered dizzy cap & rotor + 1 duff spark plug cap.

Given that Merc cap is £20 - does anyone have experience of alternative brands ie NGK?

Ta

Steve

 

[steved]

dear mercmush- you fixed it with 2 spark plugs? ? ?

How did you determine which two?
( Mine Idles rough too)
Thought I would replace all 12.

 

[steveb]

For note, all my plugs looked OK but cleaned anyway. When I checked the caps, all except one had a bright, clean connection up inside where it clips to the plug terminal thread. One cap was burnt inside, & so was plug terminal. I guessed that this was causing problem Just have to find a new cap.

 

[mercmush]

which 2 plugs

I didn't actually diagnose the problem my friend & mechanic Roger did & in answer to the other query about NGK spark plugs I have tried them previously in my 1984 500SEC and had no problems whatsoever. They were also half the price of the Bosch Super 4 plugs and NGK are maunfactured in the country of genuine quality control = Japan.