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  #1  
Old 11-28-2001, 10:14 AM
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Join Date: Oct 2001
Location: Atlanta Ga
Posts: 281
Need to resolve recent rough idle!!!

Hey guys!
This morning my 86 560 SEL was running very rough and this just started after it sat over thanksgiving weekend (and it rained).Ever since it has a very rough idle/skip type while I'm sitting at idle or at takeoff from a light to about 20-30mph but runs smooth as silk on the highway and even when it skips at idle the tach doesn't fluctuate.I'm wondering if I should take it slow and not just jump into replacing damn near everything!Any suggestions because this is a pain and feels like she really wants to quit at first but once I mash the accelerator,she's ready to play hard.Any responses would really be appreciated and thanks in advance!
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  #2  
Old 11-28-2001, 11:26 AM
raymond3
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I have (had) the same problem

It started as a very rich cold startup. The mixture was adjusted. Then the car ran great for a few days. One morning I cranked and cranked and cranked and the car wouldn't start. Finally, I figured out that if I cranked and quickly let the key go, the car would fire right up.

The car idled smooth during the warm up period but after reaching operating temp felt like it would die at stop lights. It also surged when stopped in D or R.

The shop replaced the Ignition Control Module (silver box mounted on the drivers side wheel well). This fixed the startup cranking problem but I haven't heard about the idle issue yet. I should hear today and will pass the info on.

The car is a 1985 500SEL.

Ray
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  #3  
Old 11-28-2001, 11:46 AM
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Join Date: Oct 2001
Location: Atlanta Ga
Posts: 281
Please pass on whatever happens with your situation...I'm thinking for now I'll try changing the fuel filter(s) for starters and then progress with the more extensive possibilities.I think one of the filters is under the car but don't know about any other locations of the top of my head. I'm sure I've already got half a tank of Chevron still left in her but wondering about any other possible fixes that aren't a mint to fix.
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  #4  
Old 11-28-2001, 12:25 PM
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Join Date: Jun 2001
Location: California
Posts: 324
Sounds to me like it could be a vacuum leak. Are there any other symptoms?

The last time I changed the oil on my 300E I knocked the trans vacuum line off of the intake manifold. It had a rough idle and the transmission shifted harshly. It was a piece of cake to find the problem because shifting was a good hint.

I'd take a look around in the engine bay and see if there's a vacuum line unplugged somewhere.
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  #5  
Old 11-28-2001, 04:41 PM
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Join Date: Oct 2001
Location: Atlanta Ga
Posts: 281
well, fortunately she shifts alright and I guess all of the lines should be okay since it sat for 3 days... I've heard of that though.Thanks for the input! I'll probably get my main man benzmac to do my timing chain whenever the shop opens or he can fit me into his schedule because she's got 217k miles on her and although it was changed at 135k mi, I'm pretty anal and want to get that done within the next month or two for prevent. maint. Anyway, hopefully, after I change the fuel filter, we'll see what happens.Also, don't forget to follow up with me after they finish with you raymond. I'd appreciate any other suggestions in the meantime about this idle problem.I've been in the office all day and she's been parked in the parking deck all day sitting as she does daily when I drive her into work. I'm interested to see how she's gonna act when I leave here in 30 min. (maybe she's just going thru "changes" and needs me to pay her more attention) We'll see and wish us luck!
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  #6  
Old 11-29-2001, 04:15 PM
raymond3
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I have my car out of the shop

Here's what they did:

check timing, lambda, and CO
repair vac line at manifold
replace #5 and #4 spark suppressers and plugs

intermittent failure of spark transistor box <-- replaced

She idles good now.

I hope this helps,

Ray
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  #7  
Old 11-29-2001, 04:52 PM
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Join Date: Oct 2001
Location: Atlanta Ga
Posts: 281
Was that pretty inexpensive or mint? My baby ran like crap when I left work yesterday and since she still had like half a tank left, I decided to try something...I ran her like hell on the highway (leadfoot) to get it to use up the gas (luckily I had company in the car while we went all over atlanta) Anyway, got her all the way to damn near empty and filled her up with another gas station's 93 octane (I usually use the same one) and again,hit the highway to head back to my side of town and while doing 80-90mph, the car had some sort of "kick" I could feel (I can't explain it but maybe someone will understand for some reason) and started running smoother. I thought that just maybe it was something in the gas or whatever happened to it while it sat for 3 days (and on an incline in the rain).Who knows, but after that it ran smoothly and also this morning,she started right up and the hesitation I expected wasn't there I hope I'm not jinxing myself by still assuming that "it" will come back but I still plan on changing the filters,etc and will probably do the injectors and the whole works anyway.I guess sometimes MB's need a little "laxative" to relieve the "stuff" that holds back performance.Thanks (and I still wouldn't mind some input about what other preventive stuff I can do to keep a smooth idle)
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