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Discussion Starter #1
I've read the forum for sometime, but this is my first post.

I have a '97 s500 coupe with 72,000 miles. Been a near perfect car except for inside rear view mirror shaking. But....yesterday, all of a sudden, it started running rough at idle and low rpm. Put in neutral the engine began to run smoothly above about 3000 rpm, but rough again at low rpm. Check engine light came on. Any ideas?

Thanks-
 

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Depends on the day!
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Off the top of my head, either O2 sensors or the throttle slide. But yes, go have the codes pulled first and let us know what they find.

Jonathan
 

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Discussion Starter #4
Just got the word from the shop--bad ignition coil. Shows what I know--I thought coils were a thing of the past.

Thanks for the replies.

M.D. Moore
 

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Leaky Valve Cover Causing Rough Idle / Running

This all reminds me of a 1996 s500 I was servicing. I was asked to do a general tune up on it (because it was running rough) plugs, fluids, filters etc etc as it had about 80,000 miles on it. I found that when I pulled out the drivers side bank plugs, one of the plugs was covered in oil along with the coil pack to spark plug end of the coil pack. The culpret was the valve cover o ring seals, one of them seemed to either have been put on wrong and got crushed under the valve cover during installation or heat and time warped it causing motor oil to leak into and around the spark plug and coil pack end. This caused the coil pack to short to the head instead of fire the plug and a misfire in the cylinder caused rough running.

I'm not saying this is the solution to every rough running or idling problem I'm suggesting it's another thing to check for. Signs of this may be juicy valve cover near the valve cover gasket seam, oily (probably black with dust stuck to oil) cylinder head just below the valve cover gasket and of course misfiring, rough running or idling.
 

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1973 W115 200 /8
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On the first series, with distributor caps, they should be inspected every 6 months.
And maybe replaced every 18 months..
(I just replaced one last november, and got i little rough idle, and lousy accelleration.. Cleaned both the caps and then the enigne started much easier, and it runs smooth again)
 

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1998 140.070 CL500, 1966 406.121 U65
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Just got the word from the shop--bad ignition coil. Shows what I know--I thought coils were a thing of the past.
No, you still have coils, but one on each cylinder. So the signal going to each cylinder,
is of a small voltage.

br,
syljua
 
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