Rough idle at operating temperature - Page 2 - Mercedes-Benz Forum

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post #11 of 16 (permalink) Old 02-11-2002, 07:46 PM Thread Starter
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MSD or Jacobs???

Don't have any experience with the Jacobs. I have owned 4 MSD units. The advantage of these is that it provides several rapid sparks (not just one) for each 'spark.' The MSD6A I have on the Mercedes is actually a bit too much. It will jump a 1' gap with an brilliant blue arc and a loud braaappp! You could probably weld with it. My '63 Chevy pickup has an MSD5 that has a nice 1/2' blue spark and if you can find one of those it would probably be easier on the distributor cap.
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post #12 of 16 (permalink) Old 02-14-2002, 01:24 PM Thread Starter
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Re: MSD or Jacobs???

Thanks for all the ideas. I have figured out 90% of the problem. It amazes me that the many dealers and shops that I have taken it to could not identify the problem and it ws so inexpensive to fix. There was a crack in the hose that fed to the fuel recirculating pump. These are tubelike with ports that drain from the valve cover gaskets. Retrospectively they were old and soft and when the engine was running would collapse to some degree from the vacuum inside. At any rate my theory is that the vacuum leak would expand as the engine got warm and the rubber more maleable. The improvement was amazing. I can still have a very subtle vibration in the idle when the car is in neutral now but otherwise it runs very smooth. And to think how much money I have spent chasing this. Again thanks all for your input. I may try hopping up the spark. Might be fun.<br> <br> Take care; Bill Aurich
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post #13 of 16 (permalink) Old 02-14-2002, 07:22 PM Thread Starter
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Great, Bill, but do you think you can explain more...

I am not quite sure what exactly it is what you did. Do you think you might be able to explain more in some detail? Like where the pump is and what hose and so on. Sounds like a great idea and I would like to try it on my car. Don't think it could hurt! Thanks in advance.
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post #14 of 16 (permalink) Old 02-23-2002, 02:55 PM Thread Starter
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Re: Rough idle at operating temperature

I had this problem on my '82 280SE which went away when I replaced the plugs with Bosch copper core W8DC. (The manual recommends W9D with Aussie spec pollution control gear fitted, other-wise W7D factory spec)I use LRP 98 fuel here in Australia. Car now runs as smooth as a baby's bum with no smoke. <br> <br> By the way, the old plugs looked clean and did not appear worn, so maybe one one or possiblt more were faulty. This was a cheap 'fix' !
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post #15 of 16 (permalink) Old 02-23-2002, 03:45 PM Thread Starter
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Re: Great, Bill, but do you think you can explain more...

Tobias;<br> <br> If you look parallel to the valve cover on the medial side of the cover is a rubber tube with four connections to the manifole head. They just pull up. The parallel tube is connected to the opposite side under the throttle body. On the drivers side the rubber tube connects to the (I think) recirculating pump. The other thing I noticed about rep[lacing these was that the old ones collapsed under vacuum. (ie when the engine was running). The point being they may not have been funtioning correctly even without the leak that I idntified. They were cheap to but. $17.5 a piece. Anyway worked for me. I might try running a hotter plug as well. Will give it some more thought. The car runs like new when under load. (ie in gear at idle) When in neutral I can still detect a subtle miss. Having said that it runs 95% better. Take care. Bill
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post #16 of 16 (permalink) Old 03-10-2002, 10:33 AM Thread Starter
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Rough Idle

I have a 1986 560SEL with this issue. I changed the plugs to Bosch Platinum 4's changed the cap rotor, air filters and breathers. I also changed the idle control valve for about $150. These changes made a big difference in idle, in and out of gear.
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