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560SL rough idle

24K views 27 replies 13 participants last post by  cwmoser 
#1 ·
Theres got to be someone who has had this problem or has some kind of answer. I have a 1986 560SL with the following:
*115k miles
*above idle runs great
*at idle engine shakes
*idle speed is correct RPM

Car has new plugs, wires, rotor, distributor cap, air filter.

What I have done: pulled off one plug wire at a time during idle to see if I could isolate cylinder with missfire. On seven cylinders there is a noticable change when the plug wire is removed. On the cylinder on the passenger side rearward, when I pull its plugwire there is no change in the idle. After finding this I moved a different plugwire to this position but nothing changed. I also checked for spark at this position and had spark. I am concluding the plug and wire is good. Still if I richen the mixture the car idles and drives perfect but is finicky to start - Any new ideas would be appreciated.
 
#4 ·
To check your theories on a bad injector I moved the suspect injector from cyl#4 to cyl#1 Cyl# 4 still had miss at idle. I then while at idle pulled plug wire off cyl# 1 at distributor and idle dropped I put this wire back on and idle improved - I then pulled the wire off cyl# 4 while at idle and noticed no change in idle whatsoever (still has miss)

Just for fun under the new injector arrangement I richened the mixture and idle smoothed out perfect.

What the heck could be happening here?
 
#7 ·
no question seems dumb to me at this point. With rich mixture and smooth idle if I pull off the wire for cyl# 4 the idle roughens. On initial cold startups car is smooth then after maybe 30 seconds or so rough idle appears and maybe rough is too harsh a word it just seems to have that annoying miss
 
#9 ·
slfan - 10/3/2005 3:09 PM

Since you have isolated it to #4 no matter what, plug is ok, wire is ok, fuel injector is ok: have you checked it has required fuel supply to the injector? Possibly there is a restriction somehow.
A clogged or damaged fuel line is uncommon, but not unheard of.
 
#10 ·
Had fuel line in hand yesterday and was able to blow through it - did not appear to be damaged or restricted. One curious thing though is that when I got the car someone had swapped fuel line 3 with fuel line 4 I noticed this right away and swapped it back - this was very early on when I wasn't focusing on the idle situation. Idle still wasn't pure from the start. Does anyone know exactly how the fuel dist works - whats inside.
 
#11 ·
Problem solved - opened port 4 at distributor and gave it a good flushing while engine running keeping fuel mopped up with paper towels so it wouldnt go anywhere. Put all back together and car runs perfect - Thanks for all the input!

Tom
 
#14 ·
Turns out the flush only worked briefly back to rough idle. If fuel cleaners don't work to solve rough idle there seems to be only one answer - (replacement fuel distributor), mine should arrive tomorrow. I will let you all know how it goes. I have done as much research as you can on these distributors and I think what fails in them is the rubber diaphragm inside - a pin hole develops and all of a sudden bad idle. I guess we really can't complain about a 20 year old piece of fuel saturated rubber membrane failing.
 
#16 ·
Did the new distributor end up fixing your issue? Where did you get it? How much?

Bill
 
#18 ·
This thread is 4 years old. Last post from MLSL was 2016. I don't think we're going to hear from him about how or if he solved his problem.

I have this same symptom. Had injectors tested and they were no longer giving a good spray. New injectors helped a lot but not totally. New plugs wires, dirt cap, rotor and ignition coil did nothing - I changed the just because they were old = a new tune up.

Next thing I am going to do is a smoke test looking for vacuum leaks. Probably won't get to this for a couple months and will probably start a new thread at that time.

Very interested in your efforts. You may want to start your own thread. If you do, please put a link in this thread.

Good luck..
 
#19 · (Edited)
I have a 1986 560SL with 190K miles.
Idles rough, basically I can feel vibration in cockpit. Smooth powerful acceleration.
Smoke tested, new injectors, new distributor cap and button, new spark plug wires, new spark plugs, premium non-Ethanol fuel ... my next move is to check Engine Mounts and Engine Shocks. Really also needs a new muffler.
 
#20 ·
Good feedback and appreciate the continued interest here as this seems clearly obvious a very common PROBLEM with this car. New Dist cap / rotor coming tomorrow but 99% sure it will have minimum affect. My next move will be the fuel distributor. I bought a ‘semi’ rebuild kit that comes with new seals and a membrane element (not sure of correct terminology) that according to what I’ve been reading can get small pin holes in it causing loss of fuel pressure and erratic idle. I guess we’ll see. For kicks, I’m going to replace the fuel filter which only the Lord knows when this was replaced last. While I understand it’s a cumulation of errors I’m sure, it certainly seems there exist the main culprit to this irritating problem. I pretty new to ‘threads’ here so please be patient until I get more experience here. Thanks!
 
#21 ·
Hanson. Had the similar rough idle and hesitation at lights on warmed engine- 1985 380sl. Changed filter/accumulator and also ran full can of Seafoam and Italian tune-up. Car runs perfectly for last 6 months. It was somewhat underused since it was a car my son used daily until 2 years ago when his job moved him out of state. As a do it yourself-er, my philosophy with older cars is to use simple fixes before going in big. Good luck.
 
#22 ·
Hi
Looking to solve the same rough idle on my 1986MB-560
Everything is Ok when i start, when driving.. problem only on warm idle !
3 monthes turning around no solution, seem to become more important..near to stall when stopped at a traffic light.
New cap and rotor, new air valve idle control ..
I expect to look after vacuum leak , but i Don’t know where to plug a smoke tool (?)
i’ll try to wash the inside of cold start injector,
Someone have a (genial) idee?
Rgds
Pascal.fr
 
#24 ·
Thanks Joe for your quick answer,
i remember i cleaned 2 years ago my injectors (ultrason cleaning)
I’ll use an additive cleaner (i bought one but i thought i could have running problems if there is injector problem, no?) but car did not ran for years.
you mean fuel filter,? In this case, do you think it could be necessary to change also the 2 fuel pumps?
Tk
 
#25 ·
Thanks Joe for your quick answer,
i remember i cleaned 2 years ago my injectors (ultrason cleaning)
I’ll use an additive cleaner (i bought one but i thought i could have running problems if there is injector problem, no?) but car did not ran for years.
you mean fuel filter,? In this case, do you think it could be necessary to change also the 2 fuel pumps?
Tk
No, start with the easy stuff first especially if you only drive your car sparingly. Remember, these are analog machines and they get very cranky if they're not run regularly.

Get a can of Chevron Techron - https://fr.texacolubricants.com/fr_fr/home/products/by_brand/techron.html
It looks like it can be purchased en France.

Run the tank of fuel down as low as possible, pour in a can of this stuff, and fill it up to the top.

Then, put the car into 3rd gear and monter comme la sale pute qu'elle est!

Do that for a good bit. Really don't be afraid of hurting the car. She'll love it!
Then maybe change the oil if you haven't done so (optional).

The next steps after this would be to inspect your engine ground strap underneath the car. I would remove the bolt, degrease, sand, and reattach the strap to the chassis.

If your car is still rough running come back here and we can go onto the harder steps.
 
#27 ·
Hi,
Finally i changed the plastic part( witch was craked, ) in the distributor.
After 6 monthes, idle hésitation comes back.
My sparks were dirty (4 rear)

Can somebody tell me on a 560 the injectors you have ?
Mine are BOSCH 0437502035,(grey) but i found also ..054. Could be better, (but More expensive) and ...023 better price but can’t see if it’s fit..
Thanks
 
#28 ·
I replaced the Fuel Injectors on my 1986 560SL with:
Bosch #0 437 502 054, which are MB # 000 0785 823
 
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